Specific Gravity, also known as relative density, is the ratio of the mass of a solid or liquid to the mass of an equal volume of distilled water. The standard temperature of calibration in the U.S. is 60°F/60°F. All Bellwether Specific Gravity Hydrometers listed are calibrated at 60°F/60°F. 1.000-1.070 Specific Gravity Range, 0.001 Subdivision