### Theory:

A system of units is the complete set of units, both fundamental and derived, for all kinds of physical quantities.
The common systems of units are given below:

 System Length Mass Time CGS Centimeter Gram Second MKS Meter Kilogram Second FPS Feet Pound Second

Important!
In the system of units, the first three systems of units (CGS, SI, MKS systems) are the metric systems of units. FPS is not a metric system of units, it is a British system of units.
SI Units:
The SI system is also known as the international system of units and it is abbreviated from the French word 'systeme International'.
SI system of units is the modernized and improved form of the previous system of units.

It is accepted in almost all the countries of the world. It is based on a certain set of fundamental units from which derived units are obtained by multiplication or division.

There are seven fundamental units in the SI system of units, which given below:

 S.No Fundamental quantities Unit Symbol 1 Time Seconds s 2 Mass Kilogram kg 3 Length Meter m 4 Temperature Kelvin k 5 Luminous intensity Candela cd 6 Electric current Ampere A 7 Amount of substance Mole mol