API Gravity Calculator (API to Specific Gravity)
By Santaji GadepatilinUpdated October 28, 2026
API gravity is the petroleum industry's scale for how heavy or light an oil is compared with water: higher API means lighter oil. It converts directly to specific gravity and density at 60 °F. This API gravity calculator works both ways — see what specific gravity is.
How to use the API gravity calculator
Enter the API gravity to get specific gravity and density at 60 °F, or enter specific gravity or density and press × on API gravity to convert the other way.
API gravity formula
°API = 141.5 ÷ SG − 131.5 · SG = 141.5 ÷ (°API + 131.5)
Density uses water at 60 °F (999.016 kg/m³).
API gravity of common products
| Product | Typical °API | SG |
|---|---|---|
| Heavy fuel oil | 12 | 0.986 |
| Heavy crude (e.g. Maya) | 21 | 0.928 |
| Arab Medium | 30 | 0.876 |
| Brent | 38 | 0.835 |
| WTI | 40 | 0.825 |
| Diesel | 35 | 0.850 |
| Kerosene / jet fuel | 45 | 0.802 |
| Petrol (gasoline) | 60 | 0.739 |
Crude classification
| Class | °API |
|---|---|
| Light | > 31.1 |
| Medium | 22.3 – 31.1 |
| Heavy | 10 – 22.3 |
| Extra heavy | < 10 |
Temperature correction
API gravity is defined at 60 °F (15.6 °C). Hydrometer readings at other temperatures are corrected to 60 °F with the API MPMS Chapter 11.1 tables before use.
Frequently asked questions
What is the API gravity formula?
API = 141.5 ÷ SG − 131.5, where SG is the specific gravity at 60 °F relative to water at 60 °F.
What API gravity is water?
Exactly 10 °API. Oils lighter than water have API above 10; heavier oils below 10.
What is light and heavy crude?
Light crude is above about 31.1 °API, medium 22.3–31.1 °API, heavy 10–22.3 °API and extra-heavy below 10 °API.
Why does API gravity matter?
Lighter crudes yield more petrol and diesel and sell at a higher price; API also feeds volume correction and flow measurement calculations.