API Gravity Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Fluid calculations are especially sensitive to density, viscosity, geometry, pressure conventions, and unit systems. API Gravity Calculator narrows that problem to the relationship used on this page, making the displayed api gravity easier to audit against the inputs and the governing equation.

What this calculator does

The API Gravity Calculator uses Density of crude liquid to estimate the page’s API gravity from the fluid-mechanics relationship below. It is meant for a defined geometry and property set, so the useful part is not just the headline number but also whether your density, viscosity, dimensions, pressure reference, and flow convention match the model.

How to use it

Start with the fields that actually drive this result: Density of crude liquid. Keep units consistent with the menus beside the fields and avoid mixing values measured under different conditions. After calculating, change one input at a time if you are comparing scenarios; that makes cause-and-effect much easier to see.

How the calculation works

API gravity is calculated from specific gravity at the reference condition: API = 141.5/SG − 131.5. When density is supplied, the page first estimates SG relative to its reference-water density.

Example

Using the page’s default example (Density of crude liquid = 850 kg/m³), the calculator reports API gravity of 34.806781 °API. Change one driving input at a time and confirm the result moves in the direction predicted by the equation; that is a quick way to catch a unit or mode mistake.

How to interpret the result

Higher °API corresponds to lower specific gravity under the petroleum convention; values should be interpreted at the reference temperature used for the density/SG data.

Limitations and notes

API gravity depends on reference-condition density/specific gravity. The crude-product selector does not automatically change the numerical density, so use a measured or appropriate reference density rather than relying on the label alone.