Physical properties
Fluid properties

Density, also known as mass density, is defined as the ratio of the mass of a body to its volume (SI unit: kg · m^–3; common unit: kg · dm^–3 or g · cm^–3) at 0°C and a pressure of 760 mm of mercury. Figure 1 shows the variation in water density between 0 and 100°C. Density should not be confused with density; a distinction is made between the density of solids and liquids and that of gases. The former is the ratio of the weight of a body to the weight of its volume of water, the latter is the ratio of the weight of a gas to the weight of the same volume of air under the same conditions of temperature and pressure: both are expressed by a number without unit.