When we are comparing the masses of equal volumes of different substances, we are actually comparing their density. The density of a substance is defined as its matter per unit volume.
Density = mass ÷ volume
p = m ÷ v
The SI unit for density is kilogram per cubic metre (kg m-3), or gram per cubic centimetre (g cm-3). The density of a substance gives the amount of matter contained in a unit volume of a substance, whereas the mass of a substance gives the amount of matter in the whole substance. The density of a substance determines whether it will float or sink in different liquids (or gases).
Measuring density
The volume of a liquid is often measured using a measuring cylinder.
