SI Units

SI Units – Système International d’Unités

the modern scientific system of units

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SI Units, Other Units or SI Prefixes

SI Units

Unit Symbol Quantity
ampere A electric current
becquerel Bq radioactivity
candela cd luminous intensity
coulomb C electric charge, electric flux
farad F electrical capacitance
gray Gy absorbed dose of ionizing radiation
henry H inductance
hertz Hz frequency
joule J work, energy and heat
katal kat catalytic activity
kelvin K thermodynamic temperature
kilogram kg mass
lumen lm luminous flux
lux lx illuminance
metre m length
mole mol amount of substance
newton N force
ohm Ω electric resistance, impedance, reactance
pascal Pa pressure, stress
radian rad plane angle
second s time
siemens S electrical conductance
sievert Sv radiation dose equivalent
steradian sr solid angle
tesla T magnetic flux density, magnetic induction, magnetic field strength
volt V electromotive force, electric potential, potential difference
watt W power, radiant flux
weber Wb magnetic flux

Base SI units are shown in red, all other units are derived

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Other Units

Unit Symbol Quantity / Notes
ångström Å wavelength of light, ultraviolet rays, X-rays, molecular and atomic distances
are a land measure = 100 sq metres
astronomical unit au the earth’s mean distance from the sun, about 92.9 million miles
bar bar atmospheric pressure
barn b effective cross-sectional area of a nucleus for the capture of neutrons
bel B relationship between two power levels
curie Ci former unit of radioactivity
day d time = 24 hours
degree ° angle = 1/360 of a circle = 60 minutes
degree Celsius ºC temperature = 1 kelvin
electronvolt eV energy acquired by an electron when accelerated by a potential of one volt
hectare ha land measure = 100 ares or 10000 sq metres
hour h time = 1/24 of a day = 60 minutes
knot 1 nautical mile per hour
litre L volume = 1 cubic decimetre = 1000 cubic centimetres
metric ton see tonne
minute min time = 1/60 of an hour = 60 seconds
minute angle = 1/60 of a degree = 60 seconds
nautical mile one minute of latitude measured along a meridian
neper Np ratio of two currents, two voltages, etc
oersted Oe magnetic field strength
rad rad former unit of absorbed radiation dose
rem rem former unit of radiation dosage
roentgen  / röntgen R dose of X-rays or gamma rays
second angle = 1/60 of a minute
tonne / metric ton t mass = 1000 kilograms
unified atomic mass unit u approximate mass of a hydrogen atom, a proton, or a neutron

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SI Prefixes

Prefix Symbol Exponent (base 10)
yotta Y 24
zetta Z 21
exa E 18
peta P 15
tera T 12
giga G 9
mega M 6
kilo k 3
hecto h 2
deca da 1
0
deci d -1
centi c -2
milli m -3
micro µ -6
nano n -9
pico p -12
femto f -15
atto a -18
zepto z -21
yocto y -24

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Created 11 April 2010