Systeme Internationale (SI) Units and Prefixes


SI base units
quantity name symbol definition
length meter m length of the path travelled by light in vacuum during a time interval of 1/299 792 458 second.
mass kilogram kg mass of Pt-Ir international standard kept at Sevres, France
time second s duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.
electric current ampere A the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in vacuum would produce between these conductors a force equal to 2 × 10-7 newton per meter of length.
thermodynamic temperature kelvin K the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
amount of substance mole mol the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12.
luminous intensity candela cd the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
plane angle radian rad the plane angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius
solid angle steradian sr solid angle that, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere.

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


CONVERSION FACTORS
Volumeliter
milliliter
L
mL
10-3
10-6
Lengthangstrom
inch
A
in.
10-10m
0.0254m
Masspoundlb.0.45359237 kg


SI derived units
quantity name symbol definition
frequency hertz Hz 1 / s
force newton N m kg / s²
pressure pascal Pa N / m²
energy joule J N m
power watt W J / s
electric charge coulomb C A s
electric potential volt V W / A
capacitance farad F C / V
resistance ohm captial greek
letter Omega
V / A
conductance siemens S A / V
magnetic flux weber Wb V s
magnetic flux density tesla T Wb / m²
inductance henry H Wb / A
luminous flux lumen lm cd sr
illuminance lux lx lm / m²

Unit Conversion Calculator