System of Units – Basics

Units are measurement standards. System of units is classified into two categories: Fundamental units and Derived units.

Fundamental units are further subdivided into following types:

  1. MKS - meter, kilogram, second
  2. CGS - centimeter, grams, second
  3. FPS - foot, pound, second
  4. S.I - precise form of MKS, used internationally.

Derived units are units derived from fundamental. It is a set of fundamental units which are used to express some form. Derived units are either dimensionless or a product of fundamental units.

Example: Kg/m², ft/in², psi, etc.

Fundamental Units


  • Length - millimeter; mm
  • Mass - kilogram, kg
  • Time - seconds; s
  • Temperature - Kelvin, K
  • Electric Current - Ampere; A

FPS system of units

  • Length - foot; ft
  • Mass - pound; lb
  • Time - seconds; s
  • Temperature - Fahrenheit; F 
  • Electric Current - Ampere; A


  • Length - centimeter; cm
  • Mass - gram, g
  • Time - seconds; s
  • Temperature - Celsius, C
  • Electric Current - Ampere; A


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