The density or mass density of a body is the quotient of its mass and its volume. It is usually indicated in grams per cubic centimeter; the unit kilogram per liter is commonly used for liquids. Density is determined by the material of a body and is therefore independent of its shape and size (i.e. density is a so-called intensive quantity). As the temperature increases, substances usually expand so that their density decreases. Substances with a negative thermal expansion, e.g. water, are an exception.