API Gravity Calculator

Free API Gravity Calculator — convert between specific gravity (at 60 °F) and API gravity and classify the crude.

889.3K uses Updated · 2026-05-11 Runs locally · zero upload
AD

The API Gravity Calculator converts between specific gravity (referenced to water at 60 °F) and API gravity, and classifies the fluid as light, medium, heavy or extra-heavy.

How to Use API Gravity Calculator

  1. Choose the direction — SG → API or API → SG.
  2. Enter the known value — specific gravity (e.g. 0.85) or API gravity (e.g. 35).
  3. Read the converted value — both SG and API are shown for cross-checking.
  4. See the classification — light, medium, heavy or extra-heavy crude.

Formula & Theory — API Gravity Calculator

API = (141.5 / SG) − 131.5
SG = 141.5 / (API + 131.5)

Use Cases for API Gravity Calculator

  • Petroleum trading — categorise crude quality and price brackets.
  • Refinery engineering — match feedstock to process design.
  • Pipeline operations — match pump and drag profiles to fluid density.
  • Lab analysis — convert hydrometer readings into API units.

Frequently asked questions about API Gravity Calculator

Why is the SG referenced at 60 °F?

The API standard uses 60 °F (15.56 °C) so that density values from different labs and seasons can be compared on a common temperature basis.

Does the calculator handle non-petroleum liquids?

The formulas work for any liquid, but the “light / medium / heavy” crude labels are petroleum-industry conventions.

Is higher API always better?

Higher API means lighter crude and usually higher market value, but each refinery is optimised for a specific feedstock range.

Is my data stored?

No. All calculations run locally in your browser; nothing is sent to any server.