Janka Hardness Using 

Nonstandard Specimens

David W. Green

Marshall Begel

William Nelson

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Note

FPL–RN–0303
February 2006

Green, David W.; Begel, Marshall; Nelson, William. 2006. Janka hardness 

using nonstandard specimens. Research Note FPL-RN-0303. Madison, WI: 

U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 13 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726–2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin. This article was written and prepared by U.S. 

Government employees on official time, and it is therefore in the public 

domain and not subject to copyright.

The use of trade or firm names in this publication is for reader information 

and does not imply endorsement by the United States Department of

Agriculture (USDA) of any product or service.

The USDA prohibits discrimination in all its programs and activities on the 

basis of race, color, national origin, age, disability, and where applicable, 

sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part 

of an individual’s income is derived from any public assistance program. 

(Not all prohibited bases apply to all programs.) Persons with disabilities 

who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET 

Center at (202) 720–2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence 

Avenue, S.W., Washington, D.C. 20250–9410, or call (800) 795–3272 

(voice) or (202) 720–6382 (TDD). USDA is an equal opportunity provider 

and employer.

Abstract

Janka hardness determined on 1.5- by 3.5-in. specimens 

(2×4s) was found to be equivalent to that determined using 

the 2- by 2-in. specimen specified in ASTM D 143. Data are 

presented on the relationship between Janka hardness and 

the strength of clear wood. Analysis of historical data determined using standard specimens indicated no difference 

between side hardness values determined on the radial face 

as opposed to the tangential. Analysis of historical data also 

indicated that the relationship between hardness modulus 

(HM) and Janka hardness (H) may be different for hardwood 

species than for softwood. Recommendations are given 

for ensuring that experimental procedures do not bias the 

results when testing non-standard specimens. The authors 

caution that if hardness (ASTM D 143) and hardness modulus (ASTM D 1037) are measured simultaneously for each 

ball penetration, the HM /H ratio may be different than that 

given in D 1037 because the two standards specify different 

rates of penetration. 

Keywords: Janka hardness, hardness modulus, Douglas-fir, 

2×4

Metric conversion chart

Inch–pound unit Conversion factor SI unit

inch (in.) 25.4 millimeter 

pound (lb) 0.454 kilogram

pound–force (lbf) 0.27 Newton

temperature oF (TF − 32)/1.8 temperature oC

Acknowledgments

Funding for this study was provided by the Forest Products 

Laboratory. The authors acknowledge the assistance of Timothy Nelson of the Forest Products Laboratory for specimen 

preparation and testing.

Contents

Executive Summary ............................................................. i

Introduction ..........................................................................1

Background ..........................................................................1

History of Standardization ...............................................1

Relationship of Janka Hardness to Other Properties ........2

Strength Properties .......................................................2

Specific Gravity ...........................................................3

Load Placement and Specimen Thickness ...................4

Growth Ring Orientation .............................................4

Moisture Content .........................................................5

Hardness Modulus .......................................................6

Procedures ............................................................................9

Material ............................................................................9

Testing ............................................................................10

Results and Discussion ......................................................10

Janka Hardness ...............................................................10

 Validity of Individual Values ......................................10

Analysis of Results ....................................................11

Janka Hardness and Hardness Modulus .........................11

Conclusions ........................................................................12

References ..........................................................................13
Executive Summary

Background

The Janka ball hardness test has been specified for solid 

wood in ASTM standard D 143 since 1922. The standard 

calls for a specimen with a cross section of 2 by 2 in. Unlike the tests for some properties, this standard does not 

provide an alternative size of 1 by 1 in. The standard also 

requires tests on the radial and tangential faces of the specimen, with the average of the values obtained reported as 

the hardness of the specimen. The study presented here was 

prompted by our concerns about the results obtained when 

conducting Janka hardness tests on non-standard specimens. 

Hardness tests had been conducted on 1.5- by 3.5-in. specimens (2×4s) as part of a study of the properties of lumber 

cut from small-diameter Douglas-fir trees growing in dense 

stands. 

Objectives

Our primary objective was to evaluate hardness values 

determined from tests on 1.5-in.-thick 2×4s compared to 

values that would have been obtained on standard 2-in.-

thick specimens. The study included determining the effect 

of thickness on Janka hardness as well as a critical analysis 

of historical data and information on various factors that 

might affect Janka hardness. Our secondary objective was 

to provide additional information about the relationship between Janka hardness and the hardness modulus specified in 

ASTM D 1037.

Procedures

Hardness tests were conducted using indentations on the 

wide face of 2×4s at thickness values of 1, 1.5, and 3 in. 

The 1-in. data were obtained by planing the 1.5-in. 2×4 on 

the side opposite the indentations; the 3-in. results were obtained by either “stacking” the specimen to be tested on top 

of another 2×4 or by “gluing” the 2×4 to be tested to another 

2×4. The test set-up allowed continuous recording of load as 

a function of penetration depth of the standard 0.444-in.-diameter steel ball into the specimen. Since hardness modulus 

is simply the relationship between the slope of the load and 

the penetration depth, it was possible to obtain both Janka 

hardness and hardness modulus from the same indentation.

Results

No difference in Janka hardness was found for thickness 

values of 1, 1.5, and 3 in. when the 3-in. depth was obtained 

by gluing together two 1.5-in.-thick specimens. Stacking 

two 1.5-in. specimens to obtain a 3-in. depth resulted in a 

lower hardness value than the value obtained with a glued 

specimen. An analysis of historical data for some selected 

hardwood and softwood species, including oak, indicated 

no real difference between standard hardness values with 

respect to the radial and tangential directions. We note that 

even very small “pin knots” in the projected path of the ball 

may effect hardness values and should thus be avoided. We 

also found that when using an automated routine to select 

load and deformation points off a continuous electronic record, it is important to ensure that the load reported for hardness corresponds very closely to a deformation of 0.222 in. 

For all thickness values, the data indicated a ratio of hardness modulus to Janka hardness (HM /H) of 4.9 as opposed 

to the value of 5.4 given in ASTM D 1037. This difference 

was attributed to two factors. First, the D 1037 ratio was 

originally developed by combining data for softwood and 

hardwood species. A reanalysis of the historical data indicated that whereas a ratio of 5.3 is appropriate for hardwood 

species, the ratio for softwood species should be 4.4. Second, the rate of loading specified for Janka hardness in both 

D 143 and D 1037 is 0.25 in/min, whereas D 1037 specifies 

a rate of 0.05 in/min for determining hardness modulus. 

These two properties can be determined by current specifications only by making two separate indentations for each 

property. In our tests, both Janka hardness and hardness 

modulus were measured on one indentation, using a rate of 

indentation of 0.25 in/min and resulted in an HM /H ratio of 

about 4.9. We speculate that had we determined hardness 

modulus at a rate of loading five times slower, then the ratio 

of hardness to hardness modulus would have been lower and 

more in line with the expected result. 

Conclusions

From our test results and a critical review of existing literature we conclude the following:

• Hardness values can be determined for 2×4s that are 

equivalent to those that would have been obtained by using the standard 2- by 2- by 6-in. specimen of ASTM 

D 143.

• If two pieces must be used to obtained a desired thickness, 

the pieces should be glued together.

• Continuous recording of load and deflection offers opportunities to better understand the results of Janka hardness 

tests on wood products, but care must be taken to ensure 

that the load reported is actually that at 0.222-in. 

deformation.

• There is no significant difference between hardness determined on the radial face as opposed to that determined on 

the tangential face, even for oak.

• Reanalysis of historical data indicates that the ratio of 

hardness modulus to Janka hardness may be different for 

hardwood and softwood species.

• When determining both Janka hardness (H) and hardness 

modulus (HM) on a product, it may be important to realize 

that standard procedures for these tests require determining each property at different rates of loading. This will 

affect reported values for the H /HM ratio. 

Introduction

As part of an evaluation of the properties of lumber cut from 

small-diameter Douglas-fir trees growing in dense stands 

(Green and others 2005), side hardness tests were conducted 

on nominal 2- by 4-in. lumber (hereafter called 2×4s) 

using the Janka ball hardness test procedure (ASTM D 143, 

ASTM 2005). This evaluation necessitated the use of a 

specimen having non-standard dimensions. In addition, the 

demise of our standard Janka jig (Fig. 1) provided an opportunity to measure ball penetration more precisely using 

a modern Instron (Instron Corp., Norwood, Massachusetts) 

testing machine (Fig. 2). The primary objective of this paper is to compare hardness values determined from tests on 

1.5-in.-thick 2×4s to values that would have been obtained 

on a standard 2-in.-thick specimen. The analysis includes 

determining the effect of thickness on Janka hardness as 

well as critical analysis of historic data and information on 

various factors that might affect Janka hardness. A number 

of recommendations are given to ensure that experimental 

procedures do not bias the results with non-standard specimens. Because we recorded load and penetration continuously during our Janka hardness tests, we have also included 

some information about hardness modulus determined on 

our 2×4s and the historical relationship between hardness 

modulus and Janka hardness.

Background

Hardness is a term that has different meanings to different 

people. To the design engineer, it is resistance to plastic deformation or resistance to wear. To the tester of materials, it 

is resistance to indentation. To the machinist, it is resistance 

to cutting, and to the mineralogist, it is resistance to scratching. McClintock and Argon (1968) note that while these 

meanings may appear to differ greatly from each other, the 

equivalent plastic flow stress of the material is a common 

factor in each definition. They point out that indentation 

tests differ not only with regard to the shape of the indenter 

but also in the following ways:

• By using a fixed load and measuring the resulting diameter or width of the impression at the surface (Brinell 

hardness, Vickers hardness)

• By using the contact area in computing the mean unit load 

on the indenter, or by using the projected area of the 

impression on the surface

• By using a fixed load and measuring the resulting depth 

of impression (Rockwell hardness)

• By using a variable load to produce a given depth of impression (Monotron hardness)

• By varying load on the indenter to produce impressions 

that range from macroscopic to microscopic

History of Standardization 

The path to standardization of a hardness testing procedure 

for wood in the United States appears to have started in 

1895 with the investigations of Filbert Roth, Special Agent 

in Charge of Timber Physics in the USDA Division of Forestry (predecessor of the Forest Service). In Bulletin 10, 

Roth and Fernow (1895) discuss wood hardness and show a 

rectangular piece of wood being imbedded directly into the 

Janka Hardness Using 

Nonstandard Specimens

David W. Green, Supervisory Research Engineer

Marshall Begel, Engineer

William Nelson, Supervisory Engineer

Forest Products Laboratory, Madison, Wisconsin

Figure 1—Historical equipment for ASTM D 143 test of 

Janka hardness: a, shaft of test jig; b, flexible collar; c, 

lever for “jiggling” collar; d, 0.444-in.-diameter ball drop.
2

Research Note FPL–RN–0302

side of a wood specimen (Fig. 3). In 1905, W.K. Hatt, then 

in charge of the timber test program for the Forest Service 

(Green and Evans 2001), published “Instructions to Engineers of Timber Tests.” For hardness tests, this report stated 

that “an investigation will be made to determine appropriate 

methods of test. The method contemplated involves a measurement of the width of scratch made by a prescribed tool 

under a prescribed pressure.” 

In 1906, Janka proposed a modified Brinell hardness test 

for wood (Kollmann and Côté 1968) based on the force 

required by static loading to embed a steel hemisphere with 

a diameter of 0.444 in., which corresponds to a circle with 

a projected area of 100 mm2, completely into the wood. 

In 1910, W.K. Hatt sent a letter to McGarvy Cline, Director of the newly established USDA Forest Service, Forest 

Products Laboratory (FPL), summarizing the findings of 

Janka and suggesting that FPL should have a tool made and 

should perform some preliminary experiments (unpublished 

FPL correspondence). As will be further discussed in the 

next section, the Janka hardness test became a standardized 

procedure for clear wood tested at FPL and was eventually 

adopted by the American Society for Testing and Materials 

(ASTM). This procedure first appeared in ASTM records as 

D 143–22T1 and became a standard procedure in 1927 with 

the formal adoption of D 143–27. Although originally expressed by Janka as a load divided by the projected area of 

contact, the D 143 hardness value has always been specified 

as the load (H) at a penetration of 0.222 in. 

The standard specimen is a solid piece of wood with a cross 

section of 2 by 2 in. and length of 6 in. A distinction is made 

between hardness determined on the end and on the side of 

the piece. No distinction is made between hardness on the 

radial and tangential surfaces. The standard calls for two 

indentions to be made on the tangential face and two indentions on the radial face. The average value of the force (lbf) 

determined in the four indentations is reported as the side 

hardness. The test jig for the D 143 test procedure originally 

had a collar to which the ball was attached; the ball was 

penetrated into the specimen until the collar was tightened 

against the specimen (Fig. 1). In 1948, the use of an electronic circuit indicator was added as an option for determining depth of penetration. While many other types of tests 

have been proposed for determining the hardness of solid 

wood (for example, Kollman and Côté 1968, Weatherwax 

and others 1948,2 and Doyle and Walker 1985), the Janka 

procedure has been the only method given in ASTM D 143. 

Relationship of Janka Hardness to 

Other Properties 

Strength Properties

In evaluating the results of hardness tests on 280 wood species, Janka found the following empirical relationship 

between hardness (H) and compression strength 

Figure 2—Modified Instron equipment for ASTM D 143 

test of Janka hardness. Penetration depth of Douglasfir 2×4 measured electronically. 

Figure 3—Early hardness test by Forest Service 

(Roth and Fernow 1895).

1 The term 22T indicates a tentative standard published for 

comment in 1922.

2 The report by Weatherwax and others (1948) provides references 

and some discussion of previous attempts to use other hardness test 

procedures with wood.
Janka Hardness Using Nonstandard Specimen

3

perpendicular to grain (Cperp) (Kollmann and Côté 1968):

 H = 2Cperp – 500 (kp/cm2) (1)

Although suitable only for rough calculations, the relationship proves that the Janka hardness test is really a modified 

impression test influenced by effects such as friction, shearing, and cleavage. 

Hardness as an indicator of wood strength was the focus 

of an unpublished FPL report in 1916 (Pettigrew and Newlin 1916). The authors noted that their data were based on 

6 years of testing and represented 30 to 100 tests per tree for 

a minimum of five typical trees per species. In some cases, 

60 or 70 trees were taken. (These data sets can no longer be 

identified and are not available.) The data summarized were 

average values per shipment for 48 shipments of conifers 

(about 37 species) and 91 shipments of hardwoods (about 

85 species). For green conifers, a good relationship was 

found between Janka hardness and modulus of rupture 

(MOR) (Fig. 4): 

 MOR = 72H(3/4) (2)

A good relationship was also found for green conifers 

between hardness and ultimate compressive stress (UCS) 

parallel to grain (Fig. 5): 

 UCS = 35.2H(3/4) (3)

While MOR of hardwoods generally increases with increasing hardness (Fig. 6), this relationship was considered “very 

indefinite” and “an attempt to determine strength from hardness with any degree of accuracy would be useless” (Pettigrew and Newlin 1916).

In discussing the variability of the data from green conifers, 

Pettigrew and Newlin noted that over half the average MOR 

values for the 48 groups were within 4.5% of the predicted 

values and in no case were any groups further than 20% 

from the predicted values. For green compressive strength, 

values for over half the 91 groups were within 6% of the 

predicted values and none was more than 20% from the 

prediction. The authors noted that the relationships would 

be different for dry wood and that hardness would not be a 

good grading tool for lumber containing defects, because 

knots would influence MOR and UCS but not hardness.

Specific Gravity

Janka found that hardness is approximately proportional to 

the density of the wood (Kollmann and Côté 1968). Based 

on numerous measurements, Newlin and Wilson (1919) 

determined that the relationship between hardness and specific gravity (G) may be expressed as a power formula and 

derived the following equation:

 H = AGn (lb) (4)

Newlin and Wilson gave separate coefficients, A and n, 

for green and dry wood, respectively, but did not separate 

hardwoods from softwoods. The current edition of the Wood 

Figure 4—Side hardness and modulus of rupture (MOR) 

relationship for green conifers (Pettigrew and Newlin 

1916). 

Figure 5—Side hardness and ultimate compressive 

stress (UCS) parallel to grain relationship for green 

conifers (Pettigrew and Newlin 1916).

Figure 6—Side hardness and MOR relationship for green 

hardwoods (Pettigrew and Newlin 1916).
4

Research Note FPL–RN–0302

Handbook (Forest Products Laboratory 1999) provides 

separate relationships for Janka hardness and specific gravity for green and dry hardwoods and softwoods (Table 1). 

These general relationships are shown in Figure 7. 

Figure 8 compares the general relationship for softwoods 

at 12% moisture content to the hardness data collected for 

suppressed-growth Douglas-fir (Green and others 2005). 

Load Placement and Specimen Thickness

When testing lumber, it may be necessary to determine 

the hardness of specimens less than 2 in. thick. It would 

appear obvious that as a specimen gets thinner, the stress 

field under the ball will eventually be affected by the hardness of the support surface (metal bed of testing machine in 

standard ASTM D 143 procedure). McClintock and Argon 

(1968) stated that when conducting the Brinell hardness 

test, the nearest edge of the specimen should not be closer 

than 2-1/2 impression diameters and the thickness should 

be greater than one impression diameter to obtain reliable 

readings. For the standard Janka ball, this recommendation 

indicates that the minimum specimen width would be 

2.664 in. (2.5 × 0.444 + 0.444) and the minimum depth 

0.666 in. (0.222 + 0.444).

Dohr (1946) made multiple determinations of Janka hardness using one piece of Sitka spruce with a cross section 

of 3 by 2 in. and length of 48 in. The specimen was conditioned to 12.6% moisture content and cut in such a way as 

to provide a straight-grained piece containing the same annual increment throughout its entire length. A series of 

10 indentations was made on specimens ranging from 0.5 

to 2 in. thick. The first series of 10 tests was made on the 

full 2-in. depth by distributing the hardness indentations 

throughout the length and width in such a manner as to obtain the best average for the piece. The specimen was then 

reduced in height by planing 1/4 in. from the bottom, and 

another series of tests was run. The results indicated no significant difference in average hardness with specimen thickness within the range tested (Table 2). 

Dohr also compared the hardness of a specimen with a cross 

section of 1 by 1 in. with that of the standard 2- by 2-in. 

specimen. For Sitka spruce, no great difficulty was encountered using the smaller specimen. However, with southern 

pine and Douglas-fir, a high percentage of specimens split 

during the hardness test. Results from the smaller specimens 

that did not split were equivalent to those obtained with the 

standard specimen. Because of the high incidence of splitting, the smaller specimen was not recommended for testing 

hardness.

Growth Ring Orientation

The standard hardness test (ASTM D 143, ASTM 2005) 

requires two hardness impressions be taken in the radial direction and two in the tangential direction. These values are 

then averaged to obtain the hardness value for the specimen. 

Historically, only a limited number of individual radial and 

tangential hardness values have been published. We analyzed radial as opposed to tangential hardness for selected 

species in the FPL historical data base (Table 3). These data 

Figure 7—Janka hardness and specific gravity relationship (Table 1). MC is moisture content.

Table 1. Relationship between Janka hardness 

(H) and specific gravity (G) for domestic speciesa

H = AGn Species 

group

Moisture

content A n 

Hardwood Green 3,720 2.31 

12% 3,400 2.09 

Softwood Green 1,400 1.41 

12% 1,930 1.50

a Specific gravity is based on oven-dry weight and 

 moisture content as indicated. Source: Forest Products 

 Laboratory (1999). 

Figure 8—Hardness and specific gravity relationship for 

suppressed growth Douglas-fir 2×4s (Green and others 

2005) compared to general relationship for dry softwoods (Table 1).
 5

were obtained using the standard specimen (ASTM D 143) 

after conditioning to 12% moisture content. The coefficient 

of variation of these observations averaged about 22%. As 

Table 3 indicates, the tangential values tended to be slightly 

higher than the radial values. For each specimen, we calculated the difference between hardness on the radial face and 

that on the tangential face. This information is summarized 

in the last three columns of Table 3. The mean difference 

was generally quite small (32 lbf for Douglas-fir), whereas 

the range of differences was quite large (radial–tangential 

values ranging 308 to −454 lbf for Douglas-fir). Thus, the 

differences in radial and tangential values are not significant, even for red oak. The primary reason to test both the 

radial and tangential faces appears to be to ensure a more 

representative value for each specimen. These findings are 

in agreement with the statement by Newlin and Johnson 

(1917) that “there is no consistent difference between radial 

and tangential hardness,” and the values are averaged and 

tabulated as “side hardness.” 

Moisture Content 

Below the fiber saturation point, side hardness increases 

with decreasing moisture content (Fig. 9). Weatherwax 

and others (1948) conducted tests with yellow birch and 

eastern white pine at four different moisture content levels. 

Although the results were not given in the paper, the authors 

stated that they were substantially equal to the adjustment 

recommendations for standard size specimens in ANC–18 

(Table 4) (1951). For each 1% change in moisture content, 

the “average” change in side hardness for the 16 softwoods 

listed in Table 4 would be 2.75% and for the hardwoods 

2.55%. The 1955 edition of the Wood Handbook (USDA 

1955) lists a 2.5% change in side hardness for each 1% 

change in moisture content. This is an approximate method 

based on a compound-interest-type formula once recommended as an alternative to more accurate methods that 

were harder to calculate (Markwardt and Wilson 1935). This 

approximate method is no longer recommended. For moisture content values within the range of approximately 6% to 

20%, change in hardness (H) with change in moisture 

Table 2. Effect of specimen thickness on Janka 

hardness of Sitka sprucea

Janka hardness (lbf) for various 

specimen heights (in.) 

Sample 2.00 1.75 1.50 1.25 1.00 0.75 0.625 0.500

 1 465 425 460 445 448 393 435 457

 2 433 427 450 470 435 438 413 415

 3 427 437 435 413 427 430 403 455

 4 425 420 415 442 425 450 440 418

 5 445 407 420 440 390 415 398 448

 6 432 429 450 463 427 408 425 420

 7 395 469 452 442 465 428 455 430

 8 440 438 448 455 403 454 435 422

 9 400 462 437 385 468 395 420 454

10 490 463 413 452 412 434 435 460

Average 435 438 438 441 430 425 426 438

a

 Source: Dohr (1946). 

Table 3. Radial and tangential Janka side hardness of dry specimensa

Janka side hardness (lbf)b

Radial Tangential Radial–Tangential 

Species No. of samples Mean SD Min Max Mean SD Min Max Mean Min Max 

Douglas-firc

 1,258 639 143 320 1,200 671 161 305 1,268 �32 308 �454

Sitka spruce 290 499 94 310 770 508 111 327 838 �9 357 �236

Yellow-poplar 170 540 130 308 998 558 127 305 1,055 �17 182 �230

True hickoryd

 80 2,306 341 1,147 2,957 2,228 429 1,062 2,990 +79 1,243 �768

Red oake

 145 1,308 252 700 1,895 1,335 274 760 2,255 �29 580 �897

a

 Unpublished Forest Products Laboratory data. 

b

 SD is standard deviation.

cCoast, interior north, and interior west. 

d

 Mockernut, pignut, shagbark, and shellbark hickory. 

e

 Northern red, black, scarlet, water, southern red, willow, pine, and California black oak. 

Janka Hardness Using Nonstandard Specimen
6

Research Note FPL–RN–0302

content (M) may be estimated from the following formula 

(Forest Products Laboratory 1999):

 H = H12(H12/Hgreen)[(12−M)/(Mp−12)] (5)

where 

H12 is hardness at 12% moisture content,

Hgreen hardness of green lumber,

M moisture content (%), and

Mp intersection moisture content (Table 5).

Hardness Modulus 

As previously noted, the standard Janka ball may not be 

suitable for woods of very high specific gravity (splitting) or 

for thin laminates (insufficient depth). Weatherwax and others (1948) proposed an alternative approach using the standard Janka tool that would solve these problems. With the 

standard test, the applied force initially increases roughly 

linearly with depth of penetration. Weatherwax and others 

used the slope of this line to derive what they termed a hardness modulus. As noted by Doyle and Walker (1985), this is 

basically a Brinell hardness, the value of which will differ 

only if the linear portion of the plot does not pass exactly 

through the origin. In the 1948 studies, matched specimens 

were initially prepared from laminated veneer yellow-birch 

and eastern white pine of various thickness, from 0.09 to 

1.006 in. After specimens were conditioned at 75oF and 50% 

relative humidity, the hardness modulus was determined. 

Above a thickness of 0.25 in., hardness did not change with 

increasing thickness. To provide for an adequate safety factor, all subsequent samples were made at least 0.5 in. thick. 

The hardness modulus was then determined using 11 different species of untreated wood, both normal and compressed. 

The hardness modulus was shown to vary with density in 

a manner similar to that of the standard Janka hardness 

(Fig. 10). However, no direct relationship between Janka 

hardness and hardness modulus was provided. 

Lewis (1968) investigated the relationship between hardness modulus and Janka hardness for a variety of wood and 

wood-based materials. Standard 2- by 2- by 6-in. specimens 

were manufactured using 11 species of solid wood, 9 particleboards, and 12 fiberboards. The specimens were equilibrated at 75oF and 50% relative humidity. Hardness modulus 

was determined to a penetration depth of 0.1 in. and Janka 

hardness at the standard 0.222 in.. The load for the Janka 

hardness test was applied with a uniform rate of crosshead 

travel of 0.25 in/min, while that for hardness modulus was 

0.05 in/min (as in the current standards, ASTM D 1037, 

ASTM 2005). From the reciprocal of the slope of the H

vs HM plot, it was determined that H = HM /5.4 (Fig. 11). 

Doyle and Walker (1985) call this constant relationship a 

“fortuitous” finding that results from the compensation of 

increasing load by increasing projected contact area. The 

relationship between hardness modulus and Janka hardness 

Figure 9—Effect of moisture content on Brinell hardness 

of pine (Kollmann and Côté 1968).

Figure 10—Hardness modulus (HM) and density 

relationship for three species of normal wood and 

eight species of untreated modified wood (Weatherwax and others 1948).

Figure 11—Janka hardness (H) and hardness 

modulus (HM) relationship based on average 

results for selected hardwood and softwood 

species (Lewis 1968).
7

is standardized for wood-based composites in ASTM D 

1037 (ASTM 2005). 

Beginning with the 1987 edition of the Wood Handbook, the 

relationship between Janka hardness (H) and specific gravity was determined by whether the species were hardwoods 

or softwoods. We decided to determine if the HM –H relationship also varies by species group, using Lewis’s data for 

solid wood (Tables 6 and 7). A plot of the individual values 

indicated that two tangential observations and three radial 

observations for southern pine appeared to be outliers 

(Fig. 12). Lewis did not comment on these outliers, but 

since he plotted mean values of HM and H for the combined 

data they would have had little effect on the predicted 

HM –H relationship. As can be seen from Table 8, these outliers have a profound effect on the HM –H relationship when 

the individual observations for softwoods are plotted. With 

the inclusion of the southern pine outliers, the HM –H relationship is different for radial as opposed to tangential hardness, but without the outliers the relationship is the same for 

radial and tangential hardness (Fig. 13). 

Table 4. Change in wood properties for 1% change in moisture content 

(ANC–18 1951)a

Change in property (%)b

Static bending 

Species Stress MOR MOE WMLc Cpar Cperp Shear H (side)

Hardwood 

Ash, black 8.9 6.4 3.6 1.8 8.3 6.8 5.1 4.1 

Ash, commercial white 4.1 3.5 1.4 0.4 4.7 4.8 2.9 2.4 

Basswood, American 6.8 4.8 2.9 2.6 6.5 6.6 4.2 4.2 

Beech, American 6.0 4.7 1.8 2.0 6.2 5.3 3.8 3.6 

Birch, sweet 6.4 5.0 2.3 1.2 7.1 7.2 5.0 3.6 

Birch, yellow 6.0 4.8 2.0 1.7 6.1 5.6 3.6 3.3 

Cherry, black 6.6 3.6 1.1 1.0 6.0 5.5 3.5 3.1 

Cottonwood 5.8 4.1 2.5 0.1 6.6 5.7 2.6 1.8 

Elm, rock 4.7 3.8 2.1 �0.3 5.3 6.1 3.5 2.8 

Hickory, true 4.9 4.8 2.8 �0.7 5.9 6.6 3.9 — 

Khaya (African mahogany) 3.2 2.5 1.6 �0.6 3.2 3.0 0.4 3.1 

Mahogany 2.6 1.3 0.8 �2.9 2.5 3.9 — 1.0 

Maple, sugar 5.2 4.4 1.4 1.9 5.7 7.1 3.9 3.4 

Oak, com. white and red 4.6 4.4 2.4 1.7 5.9 4.4 3.5 1.8 

Sweetgum 6.7 4.7 2.2 1.5 6.1 5.4 3.5 2.4 

Walnut, black 5.8 3.7 1.4 �2.6 4.8 6.3 1.0 1.0 

Yellow-poplar 5.0 4.6 2.7 1.9 6.7 4.8 3.3 2.4 

Softwood 

Baldcypress 4.6 4.0 1.6 1.8 4.9 5.1 1.7 2.3 

Douglas-fir 4.5 3.7 1.8 1.9 5.5 5.0 1.7 2.9 

Fir, noble 5.1 4.7 1.9 3.2 6.1 5.5 2.3 3.1 

Hemlock, western 4.7 3.4 1.4 0.7 5.0 3.7 2.5 2.0 

Incense cedar, California 3.4 2.1 1.8 �1.4 4.3 4.0 0.4 1.5 

Pine, eastern white 5.6 4.8 2.0 2.1 5.7 5.6 2.2 2.2 

Pine, red 8.0 5.7 2.2 4.7 7.5 7.2 3.9 4.5 

Pine, sugar 4.4 3.9 2.1 0.1 5.4 4.4 3.7 1.9 

Pine, western white 5.3 5.1 2.2 4.8 6.5 5.2 2.5 1.5 

Redcedar, western 4.3 3.4 1.6 1.3 5.1 5.1 1.6 2.3 

Spruce, red and Sitka 4.7 3.9 1.7 2.0 5.3 4.3 2.6 2.4 

Spruce, white 5.8 4.8 1.9 2.1 6.5 5.7 3.7 3.3 

White-cedar, northern 5.4 3.6 1.8 �1.5 5.9 2.3 2.8 3.0 

White-cedar, Port Orford 5.7 5.2 1.6 1.7 6.2 6.7 2.2 2.8 

aCorrections to strength properties should be made successively for each 1% change in 

 moisture content until total change has been covered. Thus, for hardness, HM/H12 =

 (1 + A/100)(12 � M)

, where HM is hardness at some desired moisture content M, H12 is 

 hardness at 12% moisture content (USDA 1955), and A is the factor given in Table 4. b

 Stress is fiber stress at proportional load; MOR, modulus of rupture; MOE, modulus of

 elasticity; WML, work to maximum load; Cpar and Cperp, compressive strength parallel 

 and perpendicular to grain, respectively (Cpar is maximum crushing strength); shear, 

 shearing strength parallel to grain; H, hardness. c

 Negative values indicate decrease in WML for decrease in moisture content. 

Janka Hardness Using Nonstandard Specimen
8

Research Note FPL–RN–0302

Table 5. Intersection moisture 

content (Mp) of selected speciesa

Speciesb Mp (%)

White ash 24 

Yellow birch 27 

American chestnut 24 

Douglas-fir 24 

Western hemlock 28 

Western larch 28 

Loblolly pine 21 

Longleaf pine 21 

Red pine 24 

Redwood 21 

Red spruce 27 

Sitka spruce 27 

Tamarack 24 

a

 Source: Forest Products Laboratory 

 (1999). 

b

 For other species, use Mp = 25. 

Table 6. Hardness and hardness modulus for tangential and radial faces of selected 

hardwood species and gradesa

 Hardness of selected lumber grades 

Hardness modulus (lbf/in.) Janka hardness (lbf) 

Species 

MC

(%) Loadb No. 1 No. 2 No. 3 No. 4 Avg. No. 1 No. 2 No. 3 No. 4 Avg. 

White ash 9.3 T 9,150 9,210 9,330 8,970 9,160 1,545 1,620 1,710 1,680 1,640 

R 8,050 7,690 7,870 8,000 7,900 1,510 1,440 1,420 1,450 1,460 

Hickory 8.1 T 12,800 13,300 13,000 12,800 13,000 2,370 2,450 2,480 2,550 2,460 

R 11,200 9,700 10,700 9,400 10,200 2,220 1,950 2,220 2,080 2,120 

Yellow- T 2,220 2,400 2,460 2,430 2,380 405 405 405 385 400 

poplar

9.7

R 1,890 2,050 2,030 1,820 1,950 385 370 360 335 360 

Red oak 9.2 T 5,080 5,380 4,490 5,170 5,030 1,100 1,020 1,080 1,090 1,070 

R 8,820 8,700 8,960 9,760 9,060 1,460 1,455 1,450 1,480 1,460 

Sugar maple 8.0 T 9,400 9,090 8,980 9,150 9,160 1,795 1,720 1,750 1,930 1,800 

R 9,340 7,650 7,870 7,220 8,020 1,580 1,440 1,520 1,410 1,490 

Ohia 8.2 T 10,870 10,410 11,170 10,630 10,770 2,020 2,050 2,000 2,000 2,020 

R 9,530 9,530 10,200 10,310 9,890 1,900 1,820 1,780 1,900 1,850 

a

 Source: Lewis (1968). MC is moisture content. 

b

 T is tangential, R radial. 

Table 7. Hardness and hardness modulus for tangential and radial faces of selected 

softwood species and gradesa

 Hardness of selected lumber grades 

Hardness modulus (lbf/in.) Janka hardness (lbf) 

Species 

MC

(%) Load No. 1 No. 2 No. 3 No. 4 Avg. No. 1 No. 2 No. 3 No.4 Avg. 

Redwood 7.2 T 2,380 2,310 2,170 2,120 2,240 385 405 415 425 410 

R 2,440 2,340 2,230 2,080 2,270 420 440 445 405 430 

White pine 7.3 T 2,110 3,000 2,670 2,450 2,560 430 445 430 420 430 

R 2,030 1,950 1,900 1,970 1,960 335 355 335 345 340 

Douglas-fir 10.4 T 4,270 3,980 4,460 4,000 4,180 670 750 830 730 740 

R 3,400 3,760 3,680 3,720 3,640 700 700 720 740 720 

Southern pine 9.9 T 5,610 8,760 5,080 8,330 6,940 1,145 1,115 1,330 1,215 1,200 

R 5,330 7,690 8,330 7,690 7,260 1,140 1,110 1,080 1,170 1,120 

Ponderosa pine 8.0 T 3,800 3,680 3,410 3,380 3,570 700 685 685 710 700 

R 3,450 3,120 3,720 3,500 3,450 755 715 700 710 720 

a

 Source: Lewis (1968). 
9

For hardwoods there is also no difference in the HM –H

relationship based on the direction of penetration. When 

the radial and tangential data are combined, the analysis for 

hardwoods and softwoods combined indicates that HM is 

5.3 times the value of H, a result that is very close to the 

value of 5.4 obtained by Lewis using mean values for all 

data. If the hardwood and softwood data are examined separately, the ratio for hardwoods is 5.3, the same as that given 

by Lewis. Excluding the southern pine outliers, the combined radial and tangential data for softwoods indicate that 

HM is only 4.4 times the value of H. The reason for the difference between our results and those of Lewis can be seen 

in Figure 13. When the hardwood and softwood data is combined, the large range of HM for hardwoods (almost twice 

that for softwood data) overwhelms the softwood trend and 

the combined data has a HM /H factor of 5.3. Based on this 

analysis, we conclude that a separate factor should be used 

for softwoods and hardwoods when HM is to be used to 

estimate H.

Having reviewed the background for hardness testing of 

solid-sawn and composite wood products in ASTM standards using the Janka ball procedure, we will now discuss 

observations resulting from our investigation of the Janka 

ball test for solid-sawn dimension lumber.

Procedures

Material 

As noted earlier, this study originated as a follow-up to 

hardness tests conducted on 120 Douglas-fir 2×4s cut from 

small-diameter, suppressed-growth trees (Green and others 

2005). The specimens were a random subset of 902 2×4s 

tested in bending and were cut from the undamaged ends 

of the subsample. The original hardness specimens had a 

cross section of 1.5 by 3.5 in. and were 6 in. long. The 

hardness indentations were taken on the wide (3.5-in.) 

face, and therefore the specimens had a thickness of 

1.5 in. For most of the 2×4s, the pith was located 

Figure 12—Janka hardness and hardness modulus 

relationship based on individual radial and tangential values for selected hardwoods and softwoods 

(Tables 6 and 7) (Lewis 1968).

Figure 13—Janka hardness and hardness modulus 

relationship. Data from Lewis (1968), excluding 

some southern pine results. 

Table 8. Relationship between Janka hardness (H) and hardness 

modulus (HM) calculated using data of Lewis (1968) 

Species H = A + BHM

grouping Direction Data a A B R2 Factorb

Hardwoods Tangential All 26.438 0.187 0.98 5.3 

Radial All �18.973 0.190 0.93 5.3 

Softwoods Tangential All 159.118 0.138 0.75 7.2 

Radial All 180.987 0.131 0.81 7.6 

Tangential Reduced �139.493 0.232 0.86 4.3 

Radial Reduced �93.113 0.228 0.97 4.4 

Hardwoods Both All 2.269 0.187 0.96 5.3 

Softwoods Both Reduced �105.983 0.227 0.90 4.4 

All Both Reduced 10.361 0.187 0.97 5.3 

aReduced data refer to the dropping of two tangential observations and three 

 radial observations for southern pine. 

b

 Factor = 1/B = HM /H.

Janka Hardness Using Nonstandard Specimen
10

Research Note FPL–RN–0302

somewhere in the cross section. Although indentations were 

not made directly at the pith when it was located near the 

wide surface of the sample, it was not possible to ensure 

either a purely radial or purely tangential orientation for the 

test surface. Two ball impressions were made on one side of 

each specimen. Prior to testing, the specimens were stored 

in a humidity chamber at 68oF and 68% relative humidity 

for several months. 

Testing 

Testing followed the procedures of ASTM D 143 (ASTM 

2005). Because our old test jig was worn out, we manufactured a new one that still had a 0.444-in.-diameter ball but 

that would connect to an Instron testing machine (Fig. 2).3 

Load was measured using a calibrated load cell having a 

maximum range of 2,000 lbf. Deflection was measured as 

machine crosshead movement, with its origin corresponding 

to the position of the load head at a small (less than 1 lbf) 

load. The crosshead movement could be accurately recorded 

to the nearest 0.0001 in. The sampling rate for collection of 

the electronic load–deflection data was 1/s for the 

1.5-in.-thick samples, but it was increased to 10/s for the 

other thickness levels to provide better resolution. In addition, a threshold was set to automatically record the “maximum load” at an indentation of 0.222 in. (see Discussion). 

Following the initial determination of Janka hardness on 

the 120 2×4s, 61 pieces were selected for additional testing. First, hardness tests were conducted on a 3-in.-thick 

specimen. This thickness was obtained by placing untested 

pieces of 1.5- by 3.5- by 6-in.-long 2×4s under the original 

tested specimens. These specimens will be referred to as 

“3-in. stacked” specimens. For these specimens, a second 

pair of indentations was obtained on the same face as used 

for the 1.5-in. thickness. No impressions were taken within 

two ball diameters of a previous indentation or within two 

ball diameters of the specimen edges. Following these tests, 

the original specimens were planed on the untested face to 

a thickness of 1 in. and the specimens tested again on the 

original face. 

After an analysis of the data for all three thickness values, 

we decided to test a 3-in. thickness using two 2×4s glued 

together (termed “3-in. glued”). Approximately sixty 

6-in.-long pieces of lumber from the original study remained 

in conditioned storage. Although not the same pieces as 

tested at 1, 1.5, and 3 in. (stacked), these pieces were from 

the same sample and thus would be expected to have approximately the same hardness as that of the original specimens. The pieces were glued together with a polyvinyl 

acetate adhesive and pressure applied per the manufacturer’s 

recommendations. Following gluing, twenty-nine 3-in.-thick 

specimens were available for testing. Two indentations were 

made on one face of each specimen.

For all thickness values, the slope of the load–deflection 

curve was calculated by taking a linear regression of the 

points between 20% and 40% of the load at 0.222 in. of 

penetration. These data were used to determine the hardness 

modulus. These percentages correspond fairly consistently 

to a penetration range of 0.06 to 0.10 in. This matches the 

recommendations of Lewis (1968), which were subsequently incorporated into ASTM D 1037 (ASTM 2005). 

Results and Discussion

Janka Hardness 

Validity of Individual Values 

Our Inston testing machine can be set to shut off at a prescribed amount of crosshead movement and to output both 

the measured penetration and the maximum load (Pmax) 

recorded during the test. Figure 14 shows a plot of such data 

for each impression (Pmax A and Pmax B) taken on each 2×4. 

Note that a few specimens were “outliers,” with penetration 

below 0.220 in. The recorded Pmax value was sometimes 

higher and at other times lower than the average of the 

Pmax loads at 0.222 in. of penetration. These outliers would 

probably not have been identified with the older procedure 

of “jiggling” the handle on the collar until it became tight 

(thus indicating penetration to 0.222 in.). With the electronic 

system it is sometimes possible, for example, to identify 

that a higher Pmax value occurred at a penetration lower than 

0.222 in. because the ball had penetrated a latewood band 

but the Pmax value had dropped slightly by the time 0.222 in. 

of penetration was reached. Thus, the newer procedure may 

offer additional insights into the data, but it presents challenges to ensuring that the standard is followed precisely. 

To ensure that we were using the load required by 

Figure 14—Initial load–indentation plot for Douglasfir 2×4s prior to reanalysis. Pmax indicates maximum 

load for two impressions (A, B) on each specimen.

 

3 Note that the new hardness jig still contains a handle that could be 

used to “jiggle” the collar, but this option was not used in this series 

of tests. 
11

ASTM D 143, we analyzed the load–penetration data and 

recorded the load precisely at 0.222 in. of penetration. These 

loads are the basis for the hardness values discussed in this 

paper.

Plots of the A versus B impression for all the pieces also 

helped us identify problems with an individual observation. 

We found that a larger than expected difference between 

the A and B impressions could occasionally be traced to a 

slight imperfection, usually a pin knot, somewhere beneath 

the impression location. The electronic capture of the 

load–deflection curve was found to be more sensitive than 

expected to such imperfections. Imperfections in a lumber 

sample are sometimes impossible to avoid. However, it is 

important that the cross section be inspected carefully and 

that it contain no imperfections anywhere throughout the 

thickness within about two ball diameters (say 3/4 to 1 in.) 

of the location chosen for an impression. 

Analysis of Results 

Table 9 summarizes the Janka hardness values for each 

thickness group. The average moisture content of all specimens was 12.2%. As would be expected from the literature, 

there was no significant difference between the results for 

the 1- and 1.5-in. thickness. There was also no difference 

between these results and the results for a 3-in.-thick specimen if the two pieces were glued together. A plot of hardness as a function of thickness yielded an R2 value of 0.076, 

which also confirms the lack of a significant trend between 

hardness and thickness (Fig. 15). However, the hardness 

of the 3-in. specimen obtained by simply stacking two 

1.5-in.-thick specimens together was about 13% lower than 

the mean for the 1.5-in.-thick specimen and about 18% 

lower than that for the 3-in. glued specimens. We speculate 

that perhaps the two stacked specimens did not produce perfectly flat contact surfaces. Lack of good contact between 

specimens could have allowed a slight springiness, which 

could act to slightly reduce the hardness value. Gluing is 

the method specified in ASTM D 1037 for obtaining the 

hardness of thin veneers. Our results support these 

recommendations.

Janka Hardness and Hardness Modulus 

Hardness modulus values were also obtained for each 

Douglas-fir specimen using the load–penetration data 

(Table 10). As with Janka hardness, only the results for the 

3-in. stacked specimens were significantly different. The results for the stacked specimens were about 16% lower than 

the results for the 1.5-in. specimens.

A ratio of hardness modulus (HM) to Janka hardness (H) was 

calculated for each piece to determine a factor that might be 

used to multiply by HM to estimate H (Table 11). For this 

calculation, the ratio was calculated separately for the A and 

B impressions and the overall mean values obtained. Thus, 

the sample sizes in Table 11 are twice those listed in Tables 

9 and 10. These values were then plotted and the slopes of 

the curves determined for the 1- 1.5-, and 3-in. glued specimens. As previously shown, H and HM values for the 3-in. 

stacked specimens were not the same as those for the other 

groups, so a regression relationship was not determined for 

the stacked specimens. As can be seen from Figure 16 and 

is quantified in Table 11, the relationships are the same for 

all three groups. Thus, we conclude that the relationship 

between H and HM is not a function of specimen thickness 

within the range of thickness values studied.

Table 9. Effect of specimen thickness on Janka hardness of suppressedgrowth Douglas-fir 2×4s at 12% moisture content 

Janka hardness (lbf) Thickness 

(in.)

Specimen 

type 

Sample 

sizea Mean COVb 5th 25th 50th 75th Equalityc

1.0 Solid 61 867 12.1 690 801 875 917 A 

1.5 Solid 61 858d 11.0 718 794 864 913 A 

3.0 Glued 29 902 17.2 645 792 900 941 A 

3.0 Stacked 61 743 13.3 606 670 730 800 B 

a

 Values reported are the average of A and B impressions. b

 Coefficient of variation (COV) = 100 × (standard deviation/mean). 

c

 Mean thickness values with same letter are not significantly different by Tukey 

 standardized range test at 0.05 confidence level. d

 For all 120 specimens tested at thickness of 1.5 in., mean hardness = 864 lbf 

 (Green and others 2005). 

Figure 15—Effect of thickness on hardness of 

Douglas-fir.

Janka Hardness Using Nonstandard Specimen
12

Research Note FPL–RN–0302

The mean value of the ratio for the 1.5-in.-thick pieces was 

5.07, and the overall average for the 1-, 1.5, and 3-in. glued 

specimens was 4.86 (Table 11). These ratios are higher than 

the average ratio of 4.4 that we expected from the reanalysis of the softwood data of Lewis (1968) given in Table 8. 

Two differences between our test procedure and that used 

by Lewis are notable. First, the softwood specimens tested 

by Lewis had about 8.6% moisture content, whereas moisture content of our specimens was about 12%. However, if 

we were to adjust our data to 8.6% moisture content using 

Equation (5) for both HM and H, the ratio would not change 

and thus moisture content would not help explain the difference between our expected results and the observed results. 

The second notable difference is that because we took both 

H and HM from the same impression series, the rate of loading for the calculation of both H and HM was 0.25 in/min. 

Lewis obtained H using a loading rate of 0.25 in/min, but 

obtained HM with a second impression on the same material using a loading rate of 0.05 in/min (as now specified in 

ASTM D 1037). We were unable to find specific information on the effect of loading rate on H or HM, but it is well 

known that properties perpendicular to the grain are more 

sensitive to rate of loading effects than are properties parallel to the grain. In a statistical analysis of the effect of 

five factors (species, direction of loading, rate of loading, 

moisture content, and tree) on the properties of wood in 

compression perpendicular to the grain, Bodig (1966) found 

rate of loading to be the most important single factor. Thus, 

it appears likely that our HM–H ratio would be lower had we 

tested HM at a rate five times slower, as did Lewis. 

Conclusions

From the results of our study we conclude the following: 

• Janka hardness values for Douglas-fir determined on 

1.5-in.-thick 2×4s are equivalent to those determined on 

a standard 2-in.-thick specimen.

• Continuous electronic recording of load and deflection 

data offers opportunities for more precise determination 

Table 11. Ratio of hardness modulus (HM) to Janka hardness (H) for 

suppressed-growth Douglas-fir 2×4s at 12% moisture content 

Factor = HM /H H = A + BHM Thickness 

(in.) Condition

Sample 

size Mean Min Max A B R2 Equality a

1.0 Solid 122 4.76 3.63 5.98 156.2 0.1728 0.82 A 

1.5 Solid 122 5.07 3.55 7.33 243.4 0.1409 0.67 A 

3.0 Glued 58 4.76 3.52 6.75 261.5 0.1494 0.74 A 

3.0 Stacked 122 4.83 2.82 6.16 (—b

) — — — 

a

 Equations relating H and HM with same letter are not significantly different at 0.05 

 confidence level. 

b

 Because there were significant differences between 3-in.-thick glued values and other 

 thickness values for both H and HM, it is not appropriate to evaluate the regression 

 relationship. 

Figure 16—Hardness modulus and Janka hardness relationship for different thicknesses of Douglas-fir.

Table 10. Effect of specimen thickness on hardness modulus of 

suppressed-growth Douglas-fir 2×4s at 12% moisture content 

Hardness modulus (lbf/in.) Thickness 

(in.)

Specimen 

type 

Sample 

size a Mean COV 5th 25th 50th 75th Equalityb

1.0 Solid 61 4,203 14.5 3,383 3,741 4,119 4,628 A 

1.5 Solid 61 4,382 18.8 3,357 3,444 4,304 4,757 A 

3.0 Glued 29 4,289 21.0 3,172 3,622 4,278 4,573 A 

3.0 Stacked 61 3,588 16.3 2,648 3,216 3,574 3,980 B 

a

 Values reported are average of A and B impressions. b

 Mean thickness values with same letter are not significantly different by Tukey 

 standardized range test at 0.05 confidence level. 
13

of the factors influencing Janka hardness. However, care 

should be taken to ensure that the load is recorded precisely at 0.222 in. of penetration.

• Analysis of historical data for selected species indicates 

no significant difference between Janka hardness values 

taken on radial and tangential faces, even for oak.

• Reanalysis of the 1968 data of Lewis indicates that the 

traditionally assumed H/HM ratio of 5.4 may be different 

for solid-sawn hardwoods (5.3) than for solid-sawn softwoods (4.4).

• When determining Janka hardness (H) and hardness modulus (HM) for a given material, it is important to realize 

that standardized procedures call for determining H using 

a crosshead speed of 0.25 in/min. 

(ASTM D 143) and HM at 0.05 in/min. Our results indicate that the ratio between H and HM might be significantly different if the same rate of crosshead motion were 

used for both indices.

References

ANC–18. 1951. Design of wood aircraft structures. Army–

Navy–Civil Committee on Aircraft Design Criteria. U.S. 

Government Printing Office, Washington, DC.

ASTM. 2005. Annual book of standards, Vol. 04.10. Wood. 

American Society for Testing and Materials, West Conshohoken, PA.

D 143–94. Standard methods of testing small clear specimens of timber. 

D 1037–99. Standard test methods for evaluating properties of wood-based fiber and particle panel materials.

Bodig. J. 1966. Stress–strain relationship for wood in transverse compression. Journal of Materials. 1(3):645–665.

Dohr, A.W. 1946. Results of exploratory tests to determine 

adaptability of standard hardness test to specimens of substandard cross section. Unpublished report. U.S. Department 

of Agriculture, Forest Service, Forest Products Laboratory, 

Madison, WI.

Doyle, J. and J.C.F. Walker. 1985. Indentation hardness of 

wood. Wood and Fiber Science. 17(3):369–376.

Forest Products Laboratory. 1999. Wood handbook: Wood 

as an engineering material. Gen. Tech. Rep. FPL-GTR-113. 

U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory, Madison, WI.

Green, D.W. and J.W. Evans. 2001. Evolution of standardized procedures for adjusting lumber properties for change 

in moisture content. Gen. Tech. Rep. FPL-GTR-127. U.S. 

Department of Agriculture, Forest Service, Forest Products 

Laboratory, Madison, WI.

Green, D.W., E.C. Lowell, and R. Hernandez. 2005. Structural lumber from dense stands of small-diameter Douglasfir trees. Forest Products Journal. 55(7/8):42–50.

Hatt, W.K. 1905. Instructions to engineers of timber tests. 

Circular 38. U.S. Department of Agriculture, Forest Service, 

Washington, DC.

Kollmann, F.F.P. and W.A. Côté, Jr. 1968. Principles of 

wood science and technology. I. Solid wood. Springer–

Verlag, New York.

Lewis, W.C. 1968. Hardness modulus as an alternative 

measure of hardness to the standard Janka ball for wood 

and wood-based materials. Res. Note FPL-RN-0189. U.S. 

Department of Agriculture, Forest Service, Forest Products 

Laboratory, Madison, WI.

Markwardt, L.J. and T.R.C. Wilson. 1935. Strength and related properties of woods grown in the United States. Tech. 

Bull. No. 479. U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Washington, DC.

McClintock, F.A. and A.L. Argon. 1968. Mechanical behavior of materials. Addison–Wesley Publishing Company, Inc., 

Reading, MA.

Newlin, J. and T.R.C. Wilson. 1917. Mechanical properties 

of woods grown in the United States. Bull. No. 556. U.S. 

Department of Agriculture, Forest Service, Washington, DC.

Newlin, J. and T.R.C. Wilson. 1919. The relationship of 

shrinkage and strength properties of wood to its specific 

gravity. Bull. No. 676. U.S. Department of Agriculture, 

Forest Service, Washington, DC.

Pettigrew, R.L. and J.A. Newlin. 1916. The hardness as an 

indication of the strength of timber. Unpublished report. 

U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory, Madison, WI.

Roth, F. and B.E. Fernow. 1895. Timber: An elementary 

discussion of the characteristics and properties of wood. 

Bull. No. 10. U.S. Department of Agriculture, Division of 

Forestry, Washington, DC. 

USDA. 1955. Wood handbook. Agric. Hbk. No. 72. U.S. 

Department of Agriculture, Forest Service, Forest Products 

Laboratory, Washington, DC.

Weatherwax, R.C., E.C.O. Erickson, and A.J. Stamm. 1948. 

A means of determining the hardness of wood and modified 

woods over a broad specific gravity range. ASTM Bull. 

153, TP 176-81, 84–89.

Janka Hardness Using Nonstandard Specimen