Density it the relationship between the volume and mass of a substance. Specifically, it is found by dividing the mass by the volume. The unit of density depends upon which units are used to measure mass and volume.
Mass is a measurement of how much matter there is in a substance. This is often found using the units grams or kilograms. Volume is a measurement of how much space a substance occupies. Cubic centimeters and cubic meters are typical units of volume. Therefore, density is commonly identified using the units grams per cubic centimeter or kilograms per cubic meter. Less commonly, density units reflect the American measurement system, so the label pounds per cubic foot is used.