Guide for the Use of the International System of Units (SI) 

v 

Check List for Reviewing Manuscripts

The following check list is intended to help NIST authors review the conformity of their 

manuscripts with proper SI usage and the basic principles concerning quantities and units. (The chapter or 

section numbers in parentheses indicate where additional information may be found.) 

(1)  Only SI units and those units recognized for use with the SI are used to express the values of 

quantities. Equivalent values in other units are given in parentheses following values in 

acceptable units only when deemed necessary for the intended audience. (See Chapter 2.) 

(2)  Abbreviations such as sec (for either s or second), cc (for either cm3

 or cubic centimeter), or 

mps (for either m/s or meter per second), are avoided and only standard unit symbols, SI 

prefix symbols, unit names, and SI prefix names are used. (See Sec. 6.1.8.) 

(3)  The combinations of letters “ppm,” “ppb,” and “ppt,” and the terms part per million, part per 

billion, and part per trillion, and the like, are not used to express the values of quantities. The 

following forms, for example, are used instead: 2.0 μL/L or 2.0 × 10–6 V, 4.3 nm/m or 

4.3 × 10–9 l, 7 ps/s or 7 × 10−12 t, where V, l, and t are, respectively, the quantity symbols for 

volume, length, and time. (See Sec. 7.10.3.) 

(4)  Unit symbols (or names) are not modified by the addition of subscripts or other information. 

The following forms, for example, are used instead. (See Secs. 7.4 and 7.10.2.) 

Vmax = 1000 V but not: V = 1000 Vmax 

a mass fraction of 10 % but not: 10 % (m/m) or 10 % (by weight) 

(5)  Statements such as “the length l1 exceeds the length l2 by 0.2 %” are avoided because it is 

recognized that the symbol % represents simply the number 0.01. Instead, forms such as 

“l1 = l2 (1 + 0.2 %)” or “Δ = 0.2 %” are used, where Δ is defined by the relation 

Δ = (l1 − l2)/l2. (See Sec. 7.10.2.) 

(6)  Information is not mixed with unit symbols (or names). For example, the form “the water 

content is 20 mL/kg” is used and not “20 mL H2O/kg” or “20 mL of water/kg.” (See 

Sec. 7.5.) 

(7)  It is clear to which unit symbol a numerical value belongs and which mathematical operation 

applies to the value of a quantity because forms such as the following are used. (See 

Sec. 7.7.) 

35 cm × 48 cm but not: 35 × 48 cm 

1MHz to 10 MHz or (1 to 10) MHz but not: 1 MHz – 10 MHz or 1 to 10 MHz 

20 oC to 30 oC or (20 to 30) oC but not: 20 oC – 30 oC or 20 to 30 oC 

123 g ± 2 g or (123 ± 2) g but not: 123 ± 2 g 

70 % ± 5 % or (70 ± 5) % but not: 70 ± 5 % 

240 × (1 ± 10 %) V but not: 240 V ± 10 % (one cannot add 

 240 V and 10 %)

(8)

  Unit symbols and unit names are not mixed and mathematical operations are not applied to 

unit names. For example, only forms such as kg/m3

, kg · m−3, or kilogram per cubic meter 

are used and not forms such as kilogram/m3

, kg/cubic meter, kilogram/cubic meter, kg per 

m3

, or kilogram per meter3. (See Secs. 6.1.7, 9.5, and 9.8.) 
Guide for the Use of the International System of Units (SI) 

vi 

(9)  Values of quantities are expressed in acceptable units using Arabic numerals and the 

symbols for the units. (See Sec. 7.6.) 

m = 5 kg but not: m = five kilograms or m = five kg 

the current was 15 A but not: the current was 15 amperes. 

(10)  There is a space between the numerical value and unit symbol, even when the value is used 

as an adjective, except in the case of superscript units for plane angle. (See Sec. 7.2.) 

a 25 kg sphere but not: a 25-kg sphere 

an angle of 2o3'4" but not: an angle of 2 o3 '4 " 

 

If the spelled-out name of a unit is used, the normal rules of English are applied: “a roll of 

35-millimeter film.” (See Sec. 7.6, note 3.) 

(11)  The digits of numerical values having more than four digits on either side of the decimal 

marker are separated into groups of three using a thin, fixed space counting from both the 

left and right of the decimal marker. For example, 15 739.012 53 is highly preferred to 

15739.01253. Commas are not used to separate digits into groups of three. (See Sec. 10.5.3.) 

(12)  Equations between quantities are used in preference to equations between numerical values, 

and symbols representing numerical values are different from symbols representing the 

corresponding quantities. When a numerical-value equation is used, it is properly written 

and the corresponding quantity equation is given where possible. (See Sec. 7.11.) 

(13)  Standardized quantity symbols such as those given in Refs. [4] and [5] are used, for 

example, R for resistance and Ar for relative atomic mass, and not words, acronyms, or ad 

hoc groups of letters. Similarly, standardized mathematical signs and symbols such as are 

given in Ref. [4: ISO 31-11] are used, for example, “tan x” and not “tg x.” More specifically, 

the base of “log” in equations is specified when required by writing loga x (meaning log to 

the base a of x), lb x (meaning log2 x ), ln x (meaning loge x), or lg x (meaning log10 x ). (See 

Secs. 10.1.1 and 10.1.2.) 

(14)  Unit symbols are in roman type, and quantity symbols are in italic type with superscripts and 

subscripts in roman or italic type as appropriate. (See Sec. 10.2 and Secs. 10.2.1 to 10.2.4.) 

(15)  When the word “weight” is used, the intended meaning is clear. (In science and technology, 

weight is a force, for which the SI unit is the newton; in commerce and everyday use, weight 

is usually a synonym for mass, for which the SI unit is the kilogram.) (See Sec. 8.3.) 

(16)  A quotient quantity, for example, mass density, is written “mass divided by volume” rather 

than “mass per unit volume.” (See Sec. 7.12.) 

(17)  An object and any quantity describing the object are distinguished. (Note the difference 

between “surface” and “area,” “body” and “mass,” “resistor” and “resistance,” “coil” and 

“inductance.”) (See Sec. 7.13.) 

(18)  The obsolete term normality and the symbol N, and the obsolete term molarity and the 

symbol M, are not used, but the quantity amount-of-substance concentration of B (more 

commonly called concentration of B), and its symbol cB and SI unit mol/m3 (or a related 

acceptable unit), are used instead. Similarly, the obsolete term molal and the symbol m are 

not used, but the quantity molality of solute B, and its symbol bB or mB and SI unit mol/kg 

(or a related SI unit), are used instead. (See Secs. 8.6.5 and 8.6.8.) 
NIST Special Publication 811 2008 Edition

 Ambler Thompson and Barry N. Taylor

Guide for the

Use of the International

System of Units (SI)

SI

m

K A

cd mol

kg s
National Institute of Standards and Technology Special Publication 811, 2008 Edition 

(Supersedes NIST Special Publication 811, April 1995 Edition) 

Natl. Inst. Stand. Technol. Spec. Publ. 811, 2008 Ed., 85 pages (March 2008; 2nd printing November 2008) 

CODEN: NSPUE3 

Note on 2nd printing: This 2nd printing dated November 2008 of NIST SP811 

corrects a number of minor typographical errors present in the 1st printing dated 

March 2008.