Specific gravity (sg) is a dimensionless quantity that represents the ratio of the density of a substance to the density of water at a specified temperature. For propane, the sg is typically determined at 60°F (15.6°C) and is defined as the ratio of the mass of a given volume of propane to the mass of an equal volume of water at the same temperature. The sg of propane is a useful property for determining the density of propane and for estimating its volume or mass.
