The SI unit (from the French: Système international d'unités") forms the basis of standard measurements both within the sciences and the wider world. Each of the major physical quantities has a SI unit associated with its use; others, known as derived quantities, have their units formed from combinations of these base units, to related to the formulae used to derive them.

Base Units[]

There are eight quantities which have base units associated with them; these form the basis for every other SI unit in existence.

Quantity SI Unit Unit Symbol Quantity Symbol
Length meter m l
Mass kilogram kg m
Time second s t
Electric voltage volt V v
Electric Current ampere A I
Temperature kelvin K T
Amount of Substance mole mol n
Luminous Intensity candela cd

Derived Units[]

These units are SI units which may be derived from the equation(s) used in the calculation of the quantities associated with them. They are usually given separate names and symbols in order to make their use easier.

Quantity Base Units SI Unit Unit Symbol Quantity Symbol
Area m2 Metres Squared m2 A
Volume m3 Metres Cubed m3 V
Density kg m−3 Kilograms per Metre Cubed kg m−3 ρ
Velocity m s−1 Metres per Second m s−1 v
Acceleration m s−2 Metres per Second Squared m s−2 a
Momentum kg m s−1 Kilogram Metre per Second kg m s−1 p
Moment of Inertia kg m2 Kilogram Metre Squared kg m2 I, J
Angular Momentum kg m2 s−1 Kilogram Metre Squared per Second kg m2 s−1 L
Force kg m s−2 Newton N F
Energy or Work kg m2 s−2 Joule J E, W
Power kg m2 s−3 Watt W P
Pressure or Stress kg m−1 s−2 Pascal Pa p
Surface Tension kg s−2 Newton per Metre N m−1 γ
Viscosity kg m−1 s−1 Kilogram per Metre per Second kg m−1 s−1 η
Frequency s−1 Hertz Hz ν, f