What Is a Derived Unit?

In physics, a derived unit is a unit expressed algebraically using base units. In the metric system, the SI base units for length, mass, time and electric current are respectively meter, kilogram, second and amp. Some derived units from these base units are area, volume, density, acceleration and frequency.


For example, area and volume are derived from the length unit meters because the unit of measurement for area is square meters and volume is cubic meters. Similarly, the unit measurement used for density is kilograms per cubic meter and for velocity it is meters per second. In physics, there are many other derived units, such as specific volume, electric conductivity and frequency.

Derived units can be dimensionless or expressed in terms of two base units. An example of a derived dimensionless unit is the refractive index while meters/second squared for acceleration is given using two base units.