<Tr> <Th> SI unit </Th> <Td> Unitless </Td> </Tr> <Tr> <Th> Derivations from other quantities </Th> <Td> S G true = ρ sample ρ H 2 O (\ displaystyle SG_ (\ text (true)) = (\ frac (\ rho _ (\ text (sample))) (\ rho _ (\ rm (H_ (2) O))))) </Td> </Tr> <P> Specific gravity is the ratio of the density of a substance to the density of a reference substance; equivalently, it is the ratio of the mass of a substance to the mass of a reference substance for the same given volume . Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance . The reference substance for liquids is nearly always water at its densest (at 4 ° C / 39.2 ° F); for gases it is air at room temperature (20 ° C / 68 ° F). Nonetheless, the temperature and pressure must be specified for both the sample and the reference . Pressure is nearly always 1 atm (101.325 kPa). </P> <P> Temperatures for both sample and reference vary from industry to industry . In British beer brewing, the practice for specific gravity as specified above is to multiply it by 1000 . Specific gravity is commonly used in industry as a simple means of obtaining information about the concentration of solutions of various materials such as brines, hydrocarbons, sugar solutions (syrups, juices, honeys, brewers wort, must, etc .) and acids . </P>

Specific gravity is a comparison of the weight of a substance to the weight of an equal volume of