Metric Prefixes

The metric system is a decimalised system of measurement. It is known as the International System of Units or Système international (SI), and is recognised the world over. The metric prefixes listed below precede a basic unit of measurement to indicate a multiple (or sub-multiple) of that unit.

Value	Prefix Name	Prefix Symbol
1030	quetta-	Q
1027	ronna-	R
1024	yotta-	Y
1021	etta-	Z
1018	exa-	E
1015	peta-	P
1012	tera-	T
109	giga-	G
106	mega-	M
103	kilo-	k
102	hecto-	h
10	deca-	da
10−1	deci-	d
10−2	centi-	c
10−3	milli-	m
10−6	micro-	μ
10−9	nano-	n
10−12	pico-	p
10−15	femto-	f
10−18	atto-	a
10−21	zepto-	z
10−24	yocto-	y
10−27	ronto-	r
10−30	quecto-	q

Fundamental Units

These are the seven basic SI units from which all other physical quantities are defined.

Quantity Name	Unit Name	Unit Symbol
time	second	s
length	metre	m
mass	kilogram	kg
electric current	ampere	A
thermodynamic temperature	kelvin	K
luminous intensity	candela	cd
amount of substance	mole	mol

The Celsius temperature scale is equivalent to the Kelvin temperature scale, with 0 °C = 273.15 K.

Derived Units

These units are derived from various combinations (products, quotients and powers) of the fundamental units.

Quantity	Name	Symbol	SI Base Units	Other SI Units
acceleration			m∙s−2
acceleration, angular			rad∙s−2
angle, plane	radian	rad	[dimensionless]
angle, solid	steradian	sr	[dimensionless]
area			m2
capacitance	farad	F	kg−1∙m−2∙s4⋅A2	C∙V−1
catalytic activity	katal	kat	mol∙s−1
concentration			mol∙m−3
density		ρ	kg∙m−3
electric charge	coulomb	C	s∙A
electric field strength			kg∙m∙s−3∙A−1	N∙C−1, V∙m−1
electrical conductance	siemens	S	kg−1∙m−2∙s3∙A2	A∙V−1, Ω−1
electrical potential	volt	V	kg∙m2∙s−3∙A−1	W∙A−1, J∙C−1
energy	joule	J	kg∙m2∙s−2	N∙m
entropy			kg∙m2∙s−2∙K−1	J∙K−1
force	newton	N	kg∙m∙s−2
frequency	hertz	Hz	s−1
heat	joule	J	kg∙m2∙s−2	N∙m
heat capacity			kg∙m2∙s−2∙K−1	J∙K−1
illuminance	lux	lx	cd∙sr⋅m−2
impedance	ohm	Ω	kg∙m2∙s−3∙A−2	V∙A−1
inductance	henry	H	kg∙m2∙s−2∙A−2	V∙s∙A−1
irradiance			kg∙s−3	W∙m−2
luminance			cd∙m−2
luminous flux	lumen	lm	cd∙sr
magnetic flux	weber	Wb	kg∙m2∙s−2∙A−1	V∙s
magnetic flux density	tesla	T	kg∙s−2∙A−1	V∙s∙m−2
moment of inertia			kg∙m2
momentum			kg∙m∙s−1	N∙s
momentum, angular			kg∙m2∙s−1	N∙m∙s
permeability			kg∙m∙s−2∙A−2	H∙m−1
permittivity			kg−1∙m−3∙s4∙A2	F∙m−1
power	watt	W	kg∙m2∙s−3	J∙s−1
pressure	pascal	Pa	kg∙m−1∙s−2	N∙m−2
radiant intensity			kg∙m2∙s−3∙sr−1	W∙sr−1
radiation dose	gray	Gy	m2∙s−2	J∙kg−1
radiation dose equivalent	sievert	Sv	m2∙s−2	J∙kg−1
radioactivity	becquerel	Bq	s−1
resistance	ohm	Ω	kg∙m2∙s−3∙A−2	V∙A−1
specific heat capacity			m2∙s−2∙K−1
specific volume			kg−1∙m3
stress	pascal	Pa	kg∙m−1∙s−2	N∙m−2
surface density			kg∙m−2
thermal conductivity			kg∙m∙s−3∙K−1	W∙m−1∙K−1
torque			kg∙m2∙s−2	N∙m
velocity			m∙s−1
velocity, angular			rad∙s−1
viscosity, dynamic			kg∙m−1∙s−1	N∙s∙m−2, Pa∙s
viscosity, kinematic			m2∙s−1
volume			m3
wave number			m−1
work	joule	J	kg∙m2∙s−2	N∙m

Non-SI Units

These units are often used in conjunction with SI units.

Quantity	Name	Symbol	Equivalent Value
area	hectare	ha	1 ha = 104 m2
energy	electronvolt	eV	1 eV = 1.602176634×10−19 J
length	astronomical unit	au	1 au = 149,597,870,700 m
	light year	ly	1 ly = 9,460,730,472,580,800 m
	parsec	pc	1 pc = (648,000/π) au
mass	tonne or metric ton	t	1 t = 1000 kg
plane/phase angle	degree	°	1° = (π/180) rad
	minute	′	1′ = (1/60)° = (π/10,800) rad
	second	″	1″ = (1/60)′ = (π/648,000) rad
pressure	bar	bar	1 bar = 100,000 Pa
time	day	d	1 d = 24 hr = 1440 min = 86,400 s
	hour	hr	1 hr = 60 min = 3,600 s
	minute	min	1 min = 60 s
volume	litre	l, L	1 L = 103 cm3 = 10−3 m3