What is the difference between density and relative density?

1 Answer
Shwetank Mauria
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 (kg)/m^3 and in FPS units it is (lb)/(ft)^3.

For example density of water in SI units is 1000(kg)/m^3 and in FPS unit it is 62.42796(lb)/(ft^3.

For iron it is 7874(kg)/m^3 or 491.55776(lb)/(ft^3.

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 1 and for iron it will always be 7.874 , whatever units one uses.

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