Typefaces for Symbols in Scientific Manuscripts
Most word processing software now in use at NIST is capable of producing lightface (that is, regular) or boldface letters of
the Latin or Greek alphabets in both roman (upright) and italic (sloping) types. The understandability of typed and typeset
scientific and technical publications is facilitated if symbols are in the correct typeface. The following rules are taken fromInternational Organization for Standardization (ISO) International Standard ISO 31-0:1992 to ISO 31-13:1992.
The typeface in which a symbol appears helps to define what the symbol represents. For example, irrespective of the typeface
used in the surrounding text, “A” would be typed or typeset in— italic type for the scalar quantity area:— roman type for the unit ampere:A;A;— italic boldface for the vector quantity vector potential:

A.

More specifically, the three major categories of symbols found in scientific and technical publications should be typed or typeset
in either italic or roman type, as follows:— symbols for quantities and variables : italic;— symbols for units : roman;— symbols for descriptive terms : roman.
These rules imply that a subscript or superscript on a quantity symbol is in roman type if it is descriptive (for example, if it is anumber or represents the name of a person or a particle); but it is in italic type if it represents a quantity, or is a variable such asx in E x or an index such as i in o i x i that represents a number. An index that represents a number is also called a “running number.”
The following four sections give examples of the proper typefaces for these three major categories.
Quantities and variables — italic
Symbols for quantities are italic, as are symbols for functions in general, for example, f (x ):t=3st time, s second

T = 22 K

T temperature, K kelvinr = 11 cm

r radius, cm centimeterl = 633 nm

l wavelength, nm nanometer

Constants are usually physical quantities and thus their symbols are italic; however, in general, symbols used as subscripts andsuperscripts are roman if descriptive:
NAuDe

Avogadro constant, A Avogadro
Debye temperature, D Debye
elementary charge

R molar gas constantZ
atomic number
me m mass, e electron

Running numbers and symbols for variables in mathematical equations are italic, as are symbols for parameters such as a and bthat may be considered constant in a given context:

Oxz
my=x 2 = ay 2 + bz 2i i

i=1

Symbols for vectors are boldface italic, symbols for tensors are sans-serif bold italic, and symbols for matrices are boldface italic:
A?B = C(vectors)

T(tensors)A=

Saa aa D (matrices)
11

12

21

22

Symbols used as subscripts and superscripts are italic if they represent quantities or variables:
cpp pressure

qm m masssV V solid angle

vz z z coordinate

Units — roman
The symbols for units and SI prefixes are roman:
mcm

meter
centimeter

gmg

gram
microgram

LmL

liter
milliliter(over)

Descriptive terms — roman
Symbols representing purely descriptive terms (for example, the chemical elements) are roman, as are symbols representing
mathematical constants that never change (for example, p) and symbols representing explicitly defined functions or well defined
operators (for example, G(x ) or div):
Chemical elements:
ArargonBboronCcarbon

Mathematical constants, functions, and operators:ebase of natural logarithms

Sxi

S

sum ofln x

loge

natural logarithm of

exp x

exp exponential of

sin x

sin

sine of

lg x

log10

common (decimal)
logarithm ofd x /dt d 1st derivative oflog a xlog alogarithm to thebase a of

lb x

log2

binary logarithm ofSymbols used as subscripts and superscripts are roman if descriptive:« (ir)
0ir irrationalEkk kinetic

V mlm molar, l liquid phasemB

B BohrSample equations showing correct typeF=q1 q2

F = mapV = nRT* /Sx A V m,*Aw B = x B V m,B

Ea = RT 2 d(ln k )/dT

c 1 = l –5 /[exp(c 2 / lT ) –1]

E = mc 2p̃B = lB lim (xB p / lB)

F= – grad VQ4p « 0 r 2p→0

Greek alphabet in roman and italic typeThe following table shows the proper form, in both roman and italic type, of the upper-case and lower-case letters of theGreek alphabet.
Greek alphabet in roman and italic typealphabeta
gamma
delta
epsilonzeta
etathetaiota
kappa
lambdamunu
xi
omicron
pi
rho
sigma
tau
upsilonphichipsi
omega(a)

A
B
GDEZ
H
Q, U(a)
IK
L
M
NJO
PPS
T
Y
FX
CV

abgd
«, ezhu, q (b)ik , û (b)lmnjop, Ãr, (b)styw, fxcv

A
B
G
D
E
Z
H
Q , U (a)
IKL
M
N
JO
P
P
ST
Y
FX
CV

abgd«,ezhu , q (b)ik , û (b)lmnjop, Ãr , (b)styw, fxcv

The International Organization for Standardization (ISO) gives only the first of these two letters (see ISO InternationalStandard ISO 31-0:1992).
(b)
ISO gives these two letters in the reverse order (see ISO International Standard ISO 31-0:1992).