Air-Fuel Ratio (AFR) Calculator

The Single Number That Describes a Combustion Mixture

Air-fuel ratio compresses a combustion mixture into one number: how many units of air mass are supplied per unit of fuel mass. It's the most widely used way to describe whether a mixture runs rich, lean, or right at stoichiometric.

The Formula

Worked Example

A process supplied with 220 kg of air and 15 kg of fuel:

How to Use This Calculator

1. Enter the Mass of Air supplied.
2. Enter the Mass of Fuel supplied.
3. Select Calculate to get the AFR.

Related Calculations

Need the inverse convention? See the Fuel-to-Air Ratio Calculator, or check how far this sits from stoichiometric in the Equivalence Ratio Calculator.