# What is the difference between density and relative density?

##### 1 Answer

May 23, 2016

Please see below.

#### Explanation:

The density is mass divided by volume and hence it has a unit - say in SI units it is

For example density of water in SI units is

For iron it is

**Relative density** on the contrary is the ratio of the density of certain matter with that of water. Hence, it does not have a unit, but is just a number. As such, it's value will not change when we change units, as both densities are calculated as ratio.

It is obvious that for water it is just