Metric system

The Système International d’Unités (SI), adopted in 1960,

is an international and coherent system devised to meet all

known needs for measurement in science and technology. It

consists of seven base units and the derived units formed as

products or quotients of various powers of the base units.

Note that base and derived units, when written as words, are

always written with a lower case first letter, even if the word is

derived from the name of a person.

SI Base units SI Prefixes (showing the

nine most common)

metre m length mega M  1000 000

kilogram kg mass kilo k  1000

second s time hecto h  100

ampere A electric current deca da  10

kelvin K thermodynamic deci d ÷ 10

temperature centi c ÷ 100

candela cd luminous intensity milli m ÷ 1000

mole mol amount of micro μ ÷ 1000 000

substance nano n ÷ 1000 000 000

SI Derived units

celsius °C = K temperature

coulomb C = As electric charge

farad F = C/V electric capacitance

henry H = W/A inductance

hertz Hz = c/s frequency

joule J = Ws energy

lumen lm = cd.sr luminous flux

lux lx = lm/m2 illuminance

newton N = kg/m/s2 force

ohm Ω = V/A electric resistance

pascal Pa = N/m2 pressure

siemens S = 1/Ω electric conductance

tesla T = Wb/m2 magnetic flux density

volt V = W/A electric potential

watt W = J/s power

weber Wb = Vs magnetic flux

SI Supplementary units

radian rad = unit of plane angle equal to an angle at the

centre of a circle the arc of which is equal

in length to the radius

steradian sr = unit of solid angle equal to an angle at the

centre of a sphere subtended by a part of

the surface equal in area to the square of

the radius