API Gravity Calculator — Petroleum Density
Convert between API gravity (°API) and specific gravity for any petroleum liquid. API gravity is the industry standard measure of how light or heavy a crude oil or refined product is — higher degrees mean lighter oil.
Conversion direction
Degrees API — higher value = lighter oil
- 1
Compute 141.5 ÷ SG
141.5 ÷ 0.85 = 166.4706 - 2
API gravity = ratio − 131.5
166.4706 − 131.5 = 35
How does this calculator work?
API gravity = (141.5 ÷ specific gravity) − 131.5, with specific gravity measured at 60 °F relative to water. Water = 10° API. Light crude = 31.1–45° API; heavy crude = 10–22.3°. Higher API gravity means lighter oil that floats on water and is generally easier to refine.
Formula
How this is calculated
API gravity is a scale developed by the American Petroleum Institute (API) and the National Institute of Standards and Technology (NIST) to compare petroleum liquids against water. The formula API = (141.5 / SG) − 131.5 is derived from the Baumé scale for light liquids, where SG is the specific gravity of the oil relative to water measured at 60 °F (15.6 °C). Water itself has an API gravity of approximately 10°; liquids lighter than water have higher API values, and liquids denser than water (API < 10°) will sink.
The industry uses API gravity to classify crude oils: extra-heavy crude and oil sands (< 10° API) require upgrading before they can be refined; heavy crude (10–22.3°) is harder to pump and process; medium crude (22.3–31.1°) is standard for many refineries; light crude (31.1–45°) flows easily and yields a higher proportion of gasoline and diesel; very light crude and condensates (> 45°) are the most valuable and easiest to refine. The Brent and WTI benchmark crudes are both light crudes in the 37–40° API range.
Note that API gravity is defined at 60 °F. Measurements at other temperatures must be corrected to the reference temperature using a volume correction factor (ASTM D1250 tables) before applying this formula. The density shown in kg/m³ uses 999.0 kg/m³ as the reference density of water at 15.6 °C.
Frequently asked questions
Water has a specific gravity of exactly 1.000 at 60 °F by definition, which corresponds to an API gravity of 10°. Any petroleum liquid with API gravity above 10° is lighter than water and floats; below 10° it is denser than water and sinks. Most crude oils float on water.
For conventional refining, lighter (higher API) crudes are generally more valuable because they require less processing energy and naturally contain more of the lighter, higher-value products like gasoline and jet fuel. However, some heavier crudes are abundant and cheap, and modern refineries equipped with cokers and hydrocrackers process them profitably. Market price depends on API gravity, sulphur content, refinery configuration, and transport costs together.
The API gravity scale was standardised in 1921 by the American Petroleum Institute to provide a single, consistent way to compare petroleum products across the industry — before that, different regional scales caused confusion in trade. The term "gravity" is historical; in US industry parlance, "gravity" of a liquid simply meant its density relative to water (what scientists now call specific gravity). API gravity is still used universally in petroleum trading contracts and pipeline specifications.
Also known as
TG we-Calculate Editorial Team. (2026). API Gravity Calculator — Petroleum Density [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/api-gravity-calculator
TG we-Calculate Editorial Team. "API Gravity Calculator — Petroleum Density." TG we-Calculate. 2026. https://we-calculate.com/calculator/api-gravity-calculator.
TG we-Calculate Editorial Team, "API Gravity Calculator — Petroleum Density," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/api-gravity-calculator
@misc{wecalculate_api_gravity_calculator, title = {API Gravity Calculator — Petroleum Density}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/api-gravity-calculator}}, year = {2026}, note = {TG we-Calculate} }
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