Density of a population (D) is :

Population density ($\text{D}$) is a measurement of population per unit area or unit volume. It is calculated by dividing the total number of individuals ($\text{N}$) by the total space or land area ($\text{S}$) they inhabit:
$$\text{D}=\frac{\text{N (number)}}{\text{S (space)}}$$