The density is the measure of how much dense a material is. If a body of mass \(m\) and volume \(V\) is given, its density is its mass per unit volume. Therefore, the density of the body denoted by \(\rho\) is

\[\rho = \frac{m}{V} \tag{1}\]

The SI unit of density is \(\text{kg}/\text{m}^3\). The density of a body may not be uniform throughout its volume. One example is the Earth whose density varies throughout its volume. In such a case we calculate the *average* density.

There is another term called *specific gravity* which is the ratio of the density of a material to the density of water at \({4^ \circ }C\). Therefore, the specific gravity is a dimensionless quantity without unit. The name "specific gravity" is weird as it has nothing to do with gravity but you still have to say the same name.