Density is defined as the mass per unit volume. In other words, it is how heavy something according to it's size. If something is very heavy and small in size, it means its density is high. The calculation formula:
Density = Mass / Volume.
Density unit in metric system is kilogram per cubic meters. So, if a cubic meter of water weighs 1000 kilograms, it means water density is 1000 kilograms
per cubic meter. The density of air (at sea level) is 1.225 kg/m3.