IC bureau of mines 

information circular 8333 

RINGELMANN SMOKE CHART 

(Revision of IC 7718) 

By Staff, Bureau of Mines 

UNITED STATES DEPARTMENT OF THE INTERIOR
 

BUREAU OF MINES
 

May 1967 
 

RINGELMANN SMOKE CHART 

(Revision of IC 7718) 

By Staff, Bureau of Mines 

i i i i i i i i i i i information circular 8333 

UNITED STATES DEPARTMENT OF THE INTERIOR
 

Stewart L. Udall, Secretary
 

BUREAU OF MINES
 

Walter R. Hibbard, Jr., Director
 
 

 

This publication has been cataloged as follows: 

U.S. Bureau of Mines 

Ringelmann smoke chart. [Washington] U.S. Dept. of the Interior, 

Bureau of Mines [1967] 

4 p. (U. S. Bureau of Mines. Information circular 8333)
 

Revision of I. C. 7718: Kudlich, Rudolf. Ringelmann smoke chart. 1955.
 

1. Smoke prevention. I. Ringelmann, Maximilian, 1861- . 

II. Kudlich, Rudolf. III. Title. (Series) 

TN23.U71 no. 8333 622.06173 

U. S. Dept. of the Int. Library 
CONTENTS
 

Page 

Abstract .............................................. 1
 

Introduction ............................................ 

........................... 

............................................ 

..................................... 

1
 

Description and method of preparing the chart 2
 

Use of chart 2
 

Ringelmann-chart reading 4
 
RINGELMANN SMOKE CHART
 

(Revision of IC 7718)
 

by
 

Staff, Bureau of Mines1
 

1Office of the Director of Coal Research, Washington, D.C. 

ABSTRACT 

The Ringelmann Smoke Chart fulfills an important need in smoke abatement work and in certain 

problems in the combustion of fuels. A knowledge of its history and method of preparation is, 

therefore, of interest to many. Since instructions on its use are not shown on the recent edition of the 

chart, those included in this revision of the previous Bureau of Mines publication now are a necessary 

complement to the chart. More detail regarding the use of the chart is included than was given in the 

earlier version. 

INTRODUCTION 

The Ringelmann Smoke Chart, giving shades of gray by which the density of columns of smoke 

rising from stacks may be compared, was developed by Professor Maximilian Ringelmann of Paris. 

Ringelmann, born in 1861, was professor of agricultural engineering at l'Institute National 

Agronomique and Director de la Station d'Essais de Machines in Paris in 1888, and held those 

positions for many years thereafter. 

The chart apparently was introduced into the United States by William Kent in an article 

published in Engineering News of November 11, 1897, with a comment that he had learned of it in a 

private communication from a Bryan Donkin of London. It was said to have come into somewhat 

extensive use in Europe by that time. Kent proposed in 1899 that it be accepted as the standard 

measure of smoke density in the standard code for power-plant testing that was being formulated by 

the American Society of Mechanical Engineers. 

The Ringelmann Chart was used by the engineers of the Technologic Branch of the 

U.S. Geological Survey (which later formed the nucleus of the present Bureau of Mines) in their 

studies of smokeless combustion beginning at St. Louis in 1904, and by 1910, it had been recognized 

officially in the smoke ordinance for Boston passed by the Massachusetts Legislature. 

The chart is now used as a device for determining whether emissions of smoke are within limits 

or standards of permissibility (statutes and ordinances) established and expressed with reference to the 

chart. It is widely used by law-enforcement or compliance officers in jurisdictions that have adopted 

standards based upon the chart. 
2 

In 1908, copies of the chart were prepared by the Technologic Branch of the Geological Survey 

for use by its fuel engineers and for public distribution. Upon its organization in 1910, the Bureau of 

Mines assumed this service together with the other fuel-testing activities of the Technologic Branch. 

DESCRIPTION AND METHOD OF PREPARING THE CHART 

The Ringelmann system is virtually a scheme whereby graduated shades of gray, varying by five 

equal steps between white and black, may be accurately reproduced by means of a rectangular grill of 

black lines of definite width and spacing on a white background. The rule given by Professor 

Ringelmann by which the charts may be reproduced is as follows: 

Card 0—All white. 

Card 1—Black lines 1 mm thick, 10 mm apart, leaving white spaces 9 mm square. 

Card 2—Lines 2.3 mm thick, spaces 7.7 mm square. 

Card 3—Lines 3.7 mm thick, spaces 6.3 mm square. 

Card 4—Lines 5.5 mm thick, spaces 4.5 mm square. 

Card 5—All black. 

The chart, as distributed by the Bureau of Mines, provides the shades of cards 1, 2, 3, and 4 on a 

single sheet, which are known as Ringelmann No. 1, 2, 3, and 4, respectively. A copy of the chart is 

included in this report. 

USE OF CHART 

Many municipal, state, and federal regulations prescribe smoke-density limits based on the 

Ringelmann Smoke Chart, as published by the Bureau of Mines. Although the chart was not originally 

designed for regulatory purposes, it is presently used for this purpose in many jurisdictions where the 

results obtained are accepted as legal evidence. 

While the chart still serves a useful purpose, it should be remembered that the data obtained by 

its use is empirical in nature and has definite limitations. The apparent darkness or opacity of a stack 

plume depends upon the concentration of the particulate matter in the effluent, the size of the 

particulate, the depth of the smoke column being viewed, natural lighting conditions such as the 

direction of the sun relative to the observer, and the color of the particles. Since unburned carbon is a 

principal coloring material in a smoke column from a furnace using coal or oil, the relative shade is a 

function of the combustion efficiency. 
3 

While the Ringelmann Smoke Chart has many limitations, it gives good practical results in the 

hands of well-trained operators. However, it is questionable whether results should be expressed in 

fractional units because of variations in physical conditions and in the judgement of the observers. 

To use the chart, it is supported on a level with the eye, at such a distance from the observer that 

the lines on the chart merge into shades of gray, and as nearly as possible in line with the stack. The 

observer glances from the smoke, as it issues from the stack, to the chart and notes the number of the 

chart most nearly corresponding with the shade of the smoke, then records this number with the time of 

observation. A clear stack is recorded as No. 0, and 100 percent black smoke as No. 5. 

To determine average smoke emission over a relatively long period of time, such as an hour, 

observations are usually repeated at one-fourth or one-half minute intervals. The readings are then 

reduced to the total equivalent of No. 1 smoke as a standard. No. 1 smoke being considered as 20 

percent dense, the percentage "density" of the smoke for the entire period of observation is obtained by 

the formula: 

Equivalent units of No. 1 smoke × 0.20 × 100 = percentage smoke density.

 Number of observations
 

A convenient form for recording and computing the percentage of smoke density appears at the 

end of this report. This procedure is often used on acceptance tests of fuel-burning equipment. 

The timing and extent of observations made for the purpose of determining compliance with a 

local smoke abatement ordinance depends upon the wording and smoke limitations of the ordinance. 
 

 

 

 

 

 

 

 

 

 

4 

RINGELMANN-CHART READING
 

Location . . . . . . . . . . . . . . . . . . . . . 

Hour. . . . . . . . . . . . . . . . . . . Date. . . . . . . . . . . . . . 9:00 - 10:00 a.m.

 9 0 1/4 1/2 3/4 0 1/4 1/2 3/4 Point of observation 

 0 - - - - 30 1 1 1 1 ............................... 1 - - - - 31 1 1 1 1

 2 - - - - 32 - - - - Distance to stack ................. 

3 1 1 1 1 33 - - - -

4 1 1 1 1 34 - - - - Direction of stack ................. 

5 2 2 2 2 35 1 1 1 1

 6 2 3 3 3 36 1 1 1 1 Direction of wind ................. 

 7 3 3 3 3 37 1 1 1 1

Velocity of wind ................. 8 2 2 1 1 38 1 1 - -

9 1 1 - - 39 - - - -

 Equiv. No. 1 Units 10 - - - - 40 - - - -

11 - - - - 41 - - - - 7 35 . . . . Units No. 5 ................ 12 - - - - 42 - - - -

13 - - - - 43 - - - - 7 28 . . . . Units No. 4 ................

14 - - - - 44 1 1 2 2 

15 - - - - 45 2 2 3 3 27 81 . . . . Units No. 3 ................ 16 - - - - 46 3 3 3 3 

17 - - - - 47 3 3 4 3 34 68 . . . . Units No. 2 ................ 18 - - - - 48 2 2 2 2 

19 2 2 2 2 49 2 2 2 2 52 52 . . . . Units No. 1 ................ 20 2 2 2 2 50 2 1 1 1 

21 2 2 2 2 51 1 1 1 1 113 0 . . . . Units No. 0 ................ 22 3 3 3 3 52 1 1 1 -

23 3 4 4 4 53 - - - - 240 264 . . . . Units ................ 24 4 5 5 5 54 - - - -

25 5 5 5 5 55 - - - - 264 

× 20 pct ' 26 4 4 3 3 56 - - - - 240

27 3 3 3 3 57 - - - - 22 pct . . . . . . . . . . . . . . . . Smoke density 28 2 2 1 1 58 - - - -

29 1 1 1 1 59 - - - -

Observer. . . . . . . . . . . . . . . . . . . . . . . 

Checked by. . . . . . . . . . . . . . . . . . . . . 

INT.-BU. OF MINES, PGH., PA. 10992