Density (D) is a quantity defined as mass (m) per unit volume (v): D = m ÷ v. Since these three quantities are related, you can find one of them if you know the other two. This is more helpful than it sounds because density is often a known quantity that you can look up, assuming you know the composition of the material.
Calculations are straightforward for solid objects, but things get more complicated for liquids, where density changes with temperature, and for gases, for which density is dependent on temperature and pressure.
