Density, also known as mass density or mass concentration, describes the ratio between the mass of a body and its volume. The density of liquids plays a vital role in technical applications in particular.
The thickness of a liquid is subject to influences such as atmospheric pressure and temperature. Usually, materials expand as the temperature rises, but there are exceptions, such as water. The unit of measurement for mass density is often kilogram per cubic metre (kg/m³) or, in the case of liquids, kilogram per litre (kg/l).