American Petroleum Institute (API) Gravity
The American Petroleum Institute (API) gravity, or API gravity, is a measure of how heavy or light petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. The API scale was designed so that most values would fall between 10 and 70. The formula to obtain API gravity of petroleum liquids from specific gravity is (SG) at 60°F and is given below.
141 5
APIGravity = -131.5
y SG
The specific gravity (SG) is measured using a hydrometer reading at 60°F. If product temperature is not at 60°F then a correction table is used. The specified API gravity range for fuel grade ethanol is API 46 to 49°. This corresponds to a relative density (specific gravity) range of 0.7972 to 0.7839 (the specific gravity/relative density scale is inverse to the API gravity scale). This should not be a problem for properly denatured, uncontaminated ethanol that was at least 197 proof before denaturing.