API Gravity Calculator

API gravity is the petroleum industry's standard measure of crude oil density, developed by the American Petroleum Institute. It uses an inverted scale relative to water: the higher the API gravity, the lighter the crude oil. Water has an API gravity of exactly 10, so oils with API gravity greater than 10 float on water, while those below 10 sink. The formula relating API gravity to specific gravity is API = (141.5 / SG) - 131.5, where SG is the specific gravity at 60 degrees Fahrenheit relative to water at the same temperature.

Crude oil classification based on API gravity has significant economic implications. Light crude (API > 31.1) commands premium prices because it yields more valuable products like gasoline and diesel during refining. Medium crude (22.3-31.1 API) is the most commonly traded grade worldwide, with benchmarks like WTI and Brent falling in this range. Heavy crude (10-22.3 API) and extra heavy crude (API < 10) require more complex and energy-intensive refining processes, and often trade at discounts. Extra heavy crude and bitumen from oil sands typically have API gravities below 10 and must be blended with diluents for pipeline transport.

Beyond crude oil pricing, API gravity is essential for reservoir engineering calculations including material balance, volumetric estimates, and fluid property correlations such as the Standing, Vasquez-Beggs, and Al-Marhoun PVT correlations, all of which take API gravity as an input. This calculator converts between API gravity and specific gravity, classifies the oil, and provides density in multiple unit systems commonly used in oilfield operations. All calculations run entirely in your browser with no data sent to any server. Built by Groundwork Analytics.