___________ is the ratio of an object's density to that of a reference substance.

The term specific gravity, abbreviated sp gr, refers to the ratio of a solid's or liquid's density to the density of water at 4 degrees Celsius. The term can also refer to the ratio of a gas's density to the density of dry air at standard temperature and pressure, though this is a less common specification.

The specific gravity is the ratio of an object's density to that of a reference substance. Based on its value, the specific gravity can tell us whether an object will sink or float in our reference substance.