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.