specific gravity
(relative density)

for petroleum products, the ratio of the mass of a given volume of product and the mass of an equal volume of water, at the same temperature. The standard reference temperature is 15.6°C (60°F). Specific gravity is determined by test method ASTM-D- 1298: the higher the specific gravity, the heavier the product. Specific gravity of a liquid can be determined by means of a hydrometer, a graduated float weighted at one end, which provides a direct reading of specific gravity, depending on the depth to which it sinks in the liquid. A related measurement is density, an absolute unit defined as mass per unit volume — usually expressed as kilograms per cubic meter (kg/m3). Petroleum products may also be defined in terms of API gravity (also determinable by ASTM-D-1298), in accordance with the formula:

API Gravity =	141.5	-131.5
(degree)	specifiic gravity (at 15.6/15.6 ºC)

Hence, the higher the API gravity value, the lighter the material, or the lower its specific gravity.

.