Density of any object is calculated by dividing the object's mass by its volume. Density is determined by the concentration of molecules in an object, so objects with a heavy mass in relation to a smaller volume have a higher density than objects with a lower concentration of molecules over a relatively large volume.
To determine the density of objects composed of multiple materials, the volume and mass of the different materials must first be separately determined. The different densities can then be averaged based upon the amount of each material in the larger object. Density for different types of materials may also be referred to as volumetric mass density, specific volume or bulk density.
The density of a particular material varies based upon its temperature and the surrounding air pressure. Generally, elements in a gaseous state are least dense, while elements in solid form have the highest density. The density of an object in a liquid state is above that for a gas but lower than the density for a solid. Elements are densest at low temperatures and decrease in density as the temperature increases. Moving an object from a low pressure environment to a high pressure environment condenses the molecules closer together, increasing its mass and thus also its density.