The SI units are a system of units recognized internationally and used in all scientific literature. This is a modern metric system of units deriving its name from Le Système International d'Unités in French. The SI was established in 1960 and has 7 base unit which are sufficient to express any other physical unit. There are another 22 derived units which have been named especially to make their use easier.
The 7 base units have been chosen such that none of them can be expressed as any of the others and there is no need to have another unit to express any physical quantity in the universe. The base units are meter for length, kilogram for mass, second for time, ampere for electric current, Kelvin for temperature, mole for amount of substance and candela for luminous intensity.