密度質量體積

The density of titanium (鈦) is 4.5 g/cm3, as compared with steel, 7.85 g/cm3, aluminium, 2.7 g/cm3. Hence, its density is not high.

Titanium is widely used in aircrafts because it has a strong strength-to weight ratio. Far better than aluminium.

in the equation: density = mass/volume, density is poroprtional to mass is only valide when comparing two materials of the SAME VOLUME.

In the actual fact, density of a susbtance depends on the molecular structure (atomic weight) of that substance.