The International Organization for Standardization (ISO),
International Union of Pure and Applied Chemistry (IUPAC), and
the International Union of Pure and Applied Physics (IUPAP) have
jointly developed a set of recommended symbols for physical and
chemical quantities. Consistent use of these recommended sym-
bols helps assure unambiguous scientific communication. The list
below is reprinted from Reference 1 with permission from IUPAC.
Full details may be found in the following references:
1. Ian Mills, Ed.,
Quantities, Units, and Symbols in Physical
Chemistry,
Blackwell
Scientific
Publications,
Oxford,
1988.
2. E. R. Cohen and P. Giacomo,
Symbols, Units, Nomenclature,
and
Fundamental
Constants
in
Physics
,
Document
IUPAP–25, 1987; also published in
Physica
, 146A 1–68,
1987.
3.
ISO Standards Handbook 2: Units of Measurement
,
International Organization of Standardization, Geneva,
1982.
GENERAL RULES
The value of a physical quantity is expressed as the product of a
numerical value and a unit, e.g.:
T
= 300 K
V
= 26.2 cm
3
C
p
= 45.3 J mol
-1
K
-1
The symbol for a physical quantity is always given in italic (slop-
ing) type, while symbols for units are given in roman type. Column
headings in tables and axis labels on graphs may conveniently be
written as the physical quantity symbol divided by the unit sym-
bol, e.g.:
T/K
V
/cm
3
C
p
/J mol
-1
K
-1
The values in the table or graph axis are then pure numbers.
Subscripts to symbols for physical quantities should be italic if the
subscript refers to another physical quantity or to a number, e.g.:
C
p
– heat capacity at constant pressure
B
n
– nth virial coefficient
Subscripts which have other meanings should be in roman type:
m
p
– mass of the proton
E
k
– kinetic energy
The following tables give the recommended symbols for the ma-
jor classes of physical and chemical quantities. The expression in
the Definition column is given as an aid in identifying the quantity
but is not necessarily the complete or unique definition. The SI
Unit gives one (not necessarily unique) expression for the coherent
SI unit for the quantity. Other equivalent unit expressions, includ-
ing those which involve SI prefixes, may be used.
Name
Symbol
Definition
SI unit
Space and Time
cartesian space coordinates
x, y, z
m
spherical polar coordinates
r, θ, φ
m, 1, 1
generalized coordinate
q, q
i
(varies)
position vector
r
r = xi + y
j
+ z
k
m
length
l
m
special symbols:
height
h
breadth
b
thickness
d, δ
distance
d
radius
r
diameter
d
path length
s
length of arc
s
area
A, A
s
, S
m
2
volume
V, (υ)
m
3
plane angle
α, β, γ, θ, φ…
α = s/r
rad, 1
solid angle
ω, Ω
ω = A/r
2
sr, 1
time
t
s
period
T
T = t/N
s
frequency
v, f
v = 1/T
Hz
circular frequency, angular frequency
ω
ω = 2πv
rad s
–1
, s
–1
characteristic time interval, relaxation time,
time constant
τ, T
τ = |
d
t/
dln
x|
s
angular velocity
ω
ω=
d
φ/
d
t
rad s
–1
, s
–1
velocity