API Gravity

The oil industry uses the API Gravity or Gravity scale (English units F, Metric units C).  If a fluids 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 thus a measure of the relative density of a petroleum liquid and the density of water, but it is used to compare the relative densities of petroleum liquids.

The relationship between API Gravity and specific gravity is as follows:

 

API Gravity formula
\(\large{ API_{gravity} = \frac{141.5}{SG} - 131.5  }\)
Symbol	English	Metric
\(\large{ API_{gravity} }\) = API gravity	\(\large{ deg }\)	\(\large{deg}\)
\(\large{ SG }\) = specific gravity	\(\large{ dimensionless }\)

 

So using the above equation, an oil with a specific gravity of 1.0 would have an API Gravity of (141.5 1.0) -131.5 = 10.0 degrees API.