Compare weight and volume of two bodies, respectively made of tin and lead, if they contain equal amounts of matter.
With the same amount of matter the weights of tin and lead are different with respect to their atomic mass (118.7 tin, lead, 207.2 amu), i.e. the mass of lead is in 207.2/118.7 at ~ 1.75 times bigger. The density of lead is 11.3415 g/cm3, the density of tin is 7,31 g/cm3. V1/V2 ∼ (207.2/11.34)*(7.31/118.7) ∼ 1.13 Thus, their volumes differ in 1.13 times.