About the API Gravity Calculator
API gravity converts a petroleum liquid's specific gravity at standard temperature into the oilfield scale used to classify crude and refined products. Engineers, lab technicians, traders, and students can move between API, specific gravity, and density while keeping temperature basis and sample measurement method visible.
How it works
- Enter specific gravity, density, or API value.
- Choose the density units and temperature basis used for the sample.
- Convert between API, specific gravity, and density.
- Use the classification note as a guide, not a full crude assay.
Frequently asked questions
What is the API gravity formula?
The common formula is API equals 141.5 divided by specific gravity at 60 degrees Fahrenheit, minus 131.5. Temperature correction matters when the measured density is not already at the reference temperature.
Does higher API mean heavier oil?
No. Higher API means lower specific gravity and a lighter petroleum liquid. Lower API values indicate heavier oils.
Can API gravity identify crude quality by itself?
No. API is only one property. Sulfur, viscosity, metals, acid number, distillation curve, and contaminants also affect crude value and processing behavior.
Why do hydrometer readings need temperature correction?
Petroleum liquids expand and contract with temperature. Standard methods correct observed density or gravity to a reference temperature so results can be compared.
Is API gravity used for refined products?
Yes, API gravity can be reported for refined petroleum products as well as crude oil, but specifications often require additional tests.
References
- ASTM D287 - API Gravity of Crude Petroleum and Petroleum Products by Hydrometer Method
- ASTM D1298 - Density, Relative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products