# Definition:SI Units

## Definition

The SI Units are the elements of the International System of Units.

## SI Base Units

SI base units
Name Unit symbol Dimension Symbol
metre $\mathrm m$ $\mathsf L$: Length $l$
kilogram $\mathrm {kg}$ $\mathsf M$: Mass $m$
second $\mathrm s$ $\mathsf T$: Time $t$
ampere $\mathrm A$ $\mathsf I$: Electric Current $I$
kelvin $\mathrm K$ $\Theta$: Temperature $T$
candela $\mathrm {cd}$ $\mathsf J$: Luminous Intensity $I_v$
mole $\mathrm {mol}$ $\mathsf N$: Amount of Substance $n$

## SI Derived Units

The units derived from the SI base units include the following:

 Square metre: $\displaystyle \mathrm m^2$ Cubic metre: $\displaystyle \mathrm m^3$ Newton: $\displaystyle \mathrm {kg} \, \mathrm m \, \mathrm s^{-2}$ Coulomb: $\displaystyle \mathrm A \, \mathrm s$

## Historical Note

The SI units originated in the work done by Joseph Louis Lagrange to establish a decimal system for weights and measures.

## Linguistic Note

The abbreviation SI in the term SI units is from the French Le Système International d'Unités (the International System of Units).