Water has a specific gravity of 1.0 at 60 degrees Fahrenheit. At the same temperature, jet fuel has a specific gravity of 0.82, blackstrap Molasses C has a specific gravity of 1.46 to 1.49, pure glycerine has a specific gravity of 1.26 and beer has a specific gravity of about 1.01.
The specific gravity of a substance is its density at a given temperature divided by the density of water at the same temperature. Since the unit of density in the nominator in this ratio cancels out the unit of density in the denominator, specific gravity is a unit without dimensions. Roughly speaking it is an indication of the heaviness of a liquid. Mercury, a liquid at temperatures and pressures found on Earth's surface and one of the heaviest liquids known, has a specific gravity of 13.0 at 60 degrees Fahrenheit. Ammonia is much lighter than water and has a specific gravity 0.662 at 60 degrees Fahrenheit.
A substance's specific gravity is different at different temperatures because a given temperature change typically affects a substance's density differently than the same temperature change affects water's density. A hydrometer is a device that measures specific gravity, used often in the auto industry to test radiator fluid, battery acid and Cetane levels in diesel fuel, while many beer brewers use it to test beer.