ISO Units & Symbols


Base Units

QUANTITY

NAME

SYMBOL

length

metre

m

mass

kilogram

kg

time

second

s

electric current

ampere

A

thermodynamic temperature

kelvin

K

amount of substance

mole

mol

luminous intensity

candela

cd

Supplementary Units

QUANTITY

NAME

SYMBOL

plane angle

radian

Rad

solid angle

steradian

sr

Derived Units

QUANTITY

NAME

SYMBOL

EXPRESSION

frequency

hertz

Hz

1 Hz = 1 s-1

force

newton

N

1 N = I kgm/s2

pressure

Pascal

Pa

1 Pa = 1 N/m2

energy, work,
quantity of heat

joule

J

1 J = 1 Nm

power

watt

W

1 W = 1 J/s

electric charge,
quantity of electricity

coulomb

C

1 C = 1 As

electric potential,
potential difference,
tension, electromotive force

volt

V

1 V = 1 J/C

electric capacitance

farad

F

1 F = I C/V

electric resistance

ohm

Ω

1 Ω = 1 V/A

electric conductance

siemens

S

1 S = 1-1

flux of magnetic induction,
magnetic flux

weber

Wb

1 Wb = 1 Vs

magnetic flux density,
magnetic induction

tesla

T

1 T = 1 Wb/m2

inductance

henry

H

1 H = 1 Wb/A

luminous flux

lumen

lm

1 Im = 1 cdsr

illuminance

lux

Ix

1 Ix = 1 lm/m2

Multiples of SI Units

PREFIX

SYMBOL

FACTOR

tera

T

1012  1 000 000 000 000

giga

G

109  1000 000 000

mega

M

106  1000 000

kilo

k

103  1000

hecto

h

102  100

deca

da

101  10

deci

d

10-1  0.1

centi

c

10-2  0.01

milli

m

10-3  0.001

micro

11

10-6  0.000 001

nano

n

10-9  0.000 000 001

Pico

p

10-12  0.000 000 000 001

femto

f

10-15  0.000 000 000 000 001

atto

a

10-18  0.000 000 000 000 000 001

Derived Units Without Special Names

QUANTITY

UNIT NAME

UNIT

area

square metre

m2

volume

cubic metre

m3

speed, velocity

metre per second

m/s

acceleration

metre per second squared

m/s2

specific volume

cubic metre per kilogram

m3/kg

density, mass density

kilogram per cubic metre

kg/m3

luminance

candela per square metre

cd/m2

thermal conductivity

watt per metre kelvin

W/ (m K)

specific energy

joule per kilogram

J/kg

Acceptable Non SI Units

QUANTITY

NAME

SYMBOL

DEFINITION

time

minute

min

1 min = 60 s

 

hour

h

1 h = 60 min = 3600 s

 

day

d

1 d = 24 h = 86400 s

plane angle

degree

1 = 1 (π/180) rad

 

minute

1' (1/60) = 2.909 x 10-4 rad

 

second

"

1" (1/60)' = 4.848 x 10-6 rad

volume

litre

l

1l = 1 dm3 = 10-3 m3

mass

tonne

t

1 t = 1 Mg = l03 kg