Material density, more often referred to simply as density, is a quantitative expression of the amount of mass contained per unit volume . The standard unit is the kilogram per meter cubed (kg/m 3 or kg · m -3 ).
Density is sometimes expressed in grams per centimeter cubed (g/cm 3 or gm · cm-3). Pure liquid water at a temperature of 4 degrees Celsius has a density of 1 g/cm 3 , which is the equivalent of 1 kg per 1000 cm 3 , or 1 kilogram per liter . To convert from kg/m 3 to g/cm 3 , multiply by 0.001. Conversely, to convert from g/cm 3 to kg/m 3 , multiply by 1000.
Occasionally, density is expressed in unusual units such as pounds per cubic foot, pounds per cubic inch, or metric tons per cubic meter. Expressions such as this can be confusing unless reduced to standard form for comparison. Sometimes density is expressed in relative terms as the specific gravity (sp gr), which is the ratio of the density of a given substance to the density of pure liquid water at 4 degrees Celsius.