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.

ValuePrefix NamePrefix Symbol
1024yotta-Y
1021etta-Z
1018exa-E
1015peta-P
1012tera-T
109giga-G
106mega-M
103kilo-k
102hecto-h
10deca-da
10−1deci-d
10−2centi-c
10−3milli-m
10−6micro-μ
10−9nano-n
10−12pico-p
10−15femto-f
10−18atto-a
10−21zepto-z
10−24yocto-y

Fundamental Units

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

Quantity NameUnit NameUnit Symbol
timeseconds
lengthmetrem
masskilogramkg
electric currentampereA
thermodynamic temperaturekelvinK
luminous intensitycandelacd
amount of substancemolemol

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.

QuantityNameSymbolSI Base UnitsOther SI Units
accelerationm∙s−2
acceleration, angularrad∙s−2
angle, planeradianrad[dimensionless]
angle, solidsteradiansr[dimensionless]
aream2
capacitancefaradFkg−1∙m−2∙s4⋅A2CV−1
catalytic activitykatalkatmol∙s−1
concentrationmol∙m−3
densityρkg∙m−3
electric chargecoulombCs∙A
electric field strengthkg∙m∙s−3∙A−1NC−1, V∙m−1
electrical conductancesiemensSkg−1∙m−2∙s3∙A2A∙V−1, Ω−1
electrical potentialvoltVkg∙m2∙s−3∙A−1W∙A−1, JC−1
energyjouleJkg∙m2∙s−2N∙m
entropykg∙m2∙s−2∙K−1J∙K−1
forcenewtonNkg∙m∙s−2
frequencyhertzHzs−1
heatjouleJkg∙m2∙s−2N∙m
heat capacitykg∙m2∙s−2∙K−1J∙K−1
illuminanceluxlxcd∙sr⋅m−2
impedanceohmΩkg∙m2∙s−3∙A−2V∙A−1
inductancehenryHkg∙m2∙s−2∙A−2V∙s∙A−1
irradiancekg∙s−3W∙m−2
luminancecd∙m−2
luminous fluxlumenlmcd∙sr
magnetic fluxweberWbkg∙m2∙s−2∙A−1V∙s
magnetic flux densityteslaTkg∙s−2∙A−1V∙s∙m−2
moment of inertiakg∙m2
momentumkg∙m∙s−1N∙s
momentum, angularkg∙m2∙s−1N∙m∙s
permeabilitykg∙m∙s−2∙A−2H∙m−1
permittivitykg−1∙m−3∙s4∙A2F∙m−1
powerwattWkg∙m2∙s−3J∙s−1
pressurepascalPakg∙m−1∙s−2N∙m−2
radiant intensitykg∙m2∙s−3sr−1Wsr−1
radiation dosegrayGym2∙s−2J∙kg−1
radiation dose equivalentsievertSvm2∙s−2J∙kg−1
radioactivitybecquerelBqs−1
resistanceohmΩkg∙m2∙s−3∙A−2V∙A−1
specific heat capacitym2∙s−2∙K−1
specific volumekg−1∙m3
stresspascalPakg∙m−1∙s−2N∙m−2
surface densitykg∙m−2
thermal conductivitykg∙m∙s−3∙K−1W∙m−1∙K−1
torquekg∙m2∙s−2N∙m
velocitym∙s−1
velocity, angularrad∙s−1
viscosity, dynamickg∙m−1∙s−1N∙s∙m−2, Pa∙s
viscosity, kinematicm2∙s−1
volumem3
wave numberm−1
workjouleJkg∙m2∙s−2N∙m

Non-SI Units

These units are often used in conjunction with SI units.

QuantityNameSymbolEquivalent Value
areahectareha1 ha = 104 m2
energyelectronvolteV1 eV = 1.602176634×10−19 J
lengthastronomical unitau1 au = 149,597,870,700 m
light yearly1 ly = 9,460,730,472,580,800 m
parsecpc1 pc = (648,000/π) au
masstonne or metric tont1 t = 1000 kg
plane/phase angledegree°1° = (π/180) rad
minute1 = (1/60)° = (π/10,800) rad
second1 = (1/60) = (π/648,000) rad
pressurebarbar1 bar = 100,000 Pa
timedayd1 d = 24 hr = 1440 min = 86,400 s
hourhr1 hr = 60 min = 3,600 s
minutemin1 min = 60 s
volumelitrel, L1 L = 103 cm3 = 10−3 m3