API gravity converter
Convert between API gravity and specific gravity, and see whether crude is lighter or heavier.
Quick answer: API gravity = 141.5 ÷ specific gravity − 131.5. Water is 10°API; crude above 31.1°API is called light and crude below 22.3°API is heavy.
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Read API gravity like a crude buyer
How to use this calculator
- Choose whether you are starting from API gravity or specific gravity.
- Enter the value measured at the standard 60°F reference temperature.
- Read the result, the density estimate and the light, medium or heavy band.
The prefilled 35°API converts to a specific gravity of about 0.850, because 141.5 ÷ (35 + 131.5) = 0.8498. That is light crude. Switch to specific-gravity mode and enter 0.934 to see a heavier crude of about 20°API.
What the number means
API gravity compares a crude oil’s density with water, which is 10°API. Oil above 10°API is lighter than water and floats. Oil below 10°API is heavier and sinks.
Light, medium and heavy
This tool uses common bands: above 31.1°API is light, 22.3–31.1°API is medium, 10–22.3°API is heavy and below 10°API is extra-heavy.
Why buyers care
Lighter crude usually yields more gasoline and diesel with less processing. Heavier crude needs more complex equipment, such as cokers, to make the same products.
Where to go next
See where real grades sit on the density and sulfur chart in the crude oil quality guide. The density you find here feeds straight into the barrels-to-tonnes converter.
Questions about this calculation
Is a higher API gravity always better?
Not always. Higher API crude is lighter and usually yields more light products, but each refinery is built for a particular mix of crudes, and price depends on much more than density.
What is the API gravity of WTI and Brent?
Both are light benchmarks. The grade data on this site places WTI at about 37–42°API and Brent at about 37–39°API.
How do I turn API gravity into kg/m³?
Convert to specific gravity first, then multiply by the density of water at 60°F, about 999 kg/m³. A 35°API crude is about 849 kg/m³.
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