base unit

A base unit is a unit that is defined arbitrarily rather in terms of combinations of simpler units. There are seven base units in the SI system, as listed in the table below. In addition, the SI system has two dimensionless (or supplementary) units – the radian and the steradian.


SI base units
mass kilogram kg
length meter m
time second s
current ampere A
amount of substance mole mol
temperature kelvin K
luminous intensity candela cd


Compare with derived unit.