Volumetric mass density is a substance’s mass per unit of volume. The mathematical formula is ρ = m / V where ρ is the density, m is the mass, and V is the volume.
Relative density is sometimes used to simplify comparisons of density across different systems of units. This refers to the ratio of a material’s density in relation to that of a standard material, usually water. If the relative density of the material is less than one relative to water, it means the material will float in water (except in cases where it mixes with water).
Pressure and temperature affect the density of a material. An increase in pressure causes a decrease in volume and therefor the density of the object is increased. For most substances, an increase in temperature will decrease the density by increasing the volume.