A substance’s specific gravity is the ratio of that substance’s density to the density of water at 4 degrees Celsius. Because the density of water at 4 degrees Celsius is 1,000 kg/m3, that ratio is easy to find. Specific gravity has no units because it’s a ratio of density divided by density, so all units cancel out. Anything with a density greater than 1,000 sinks in pure water at 4 degrees Celsius, and anything with a density less than 1,000 floats. |