The American Petroleum Institute gravity, or API Thermo-hydrometer, is a measure of how heavy or light a 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.
API gravity is an inverse measure of a petroleum liquid's density relative to that of water.
It is used to compare densities of petroleum liquids. For example, if one petroleum liquid is less dense than another, it has a greater API gravity.
Although API gravity is mathematically a dimensionless quantity, it is referred to as being in 'degrees'. API gravity is graduated in degrees on a hydrometer instrument. API gravity values of most petroleum liquids fall between 10 and 70 degrees.
Thermo-hydrometers conform to ASTM specifications. Unit includes thermometer in the body. Temperature of standardization is 60 degree F. 0.1 degree division. 380mm Length. Thermometer Range 0 to 150 degree F. 49 to 61 API Range.