NOTE 1 Mass density is an intensive quantity describing a local property of a substance.

NOTE 2 The concept of mass density may also be applied to the mass m in a domain D with volume V, leading to the average density ${\displaystyle {\rho }_{\text{av}}=\frac{m}{V}=\frac{1}{V}\underset{\text{D}}{\int }\rho dV}$.

NOTE 3 The coherent SI unit of mass density is kilogram per cubic metre, kg/m³. Other units are tonne per cubic metre, t/m³ (1 t/m³ = 1 000 kg/m³ = 1 g/cm³), and kilogram per litre, kg/l (1 kg/l = 1 000 kg/m³).