The ratio of mass to volume of a substance is called density. Units of measure for density include kilograms per meter cubed and grams per centimeter cubed.
Density of a substance is a useful property as it determines whether the substance can float on water. If the density of a substance is less than the density of water, it floats on water; else, it sinks. The density of water is 1 gram per centimeter cubed. It is used as a standard in calculating relative densities of various substances. Relative density is defined as the ratio of the density of a substance to the density of water.