Air Fuel Ratio Calculator

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Determine the mass ratio of air to fuel in a combustion process.

Mixture Parameters

Mass of Air

Mass of Fuel

Calculation Results

Enter the masses of air and fuel to calculate the ratio

About this calculator

Overview

The air-fuel ratio (AFR) is the mass ratio of air to a solid, liquid, or gaseous fuel present in a combustion process.

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Pro Tips

AFR affects both engine performance and exhaust emissions.
Stoichiometric combustion is the ideal process where all fuel is burned with all available air.
Diesel engines typically operate at much leaner ratios than gasoline engines.

Lambda (λ) and Equivalence Ratio (φ)

Engineers often use Lambda (λ), which is the ratio of actual AFR to stoichiometric AFR. λ = 1 is stoichiometric, λ < 1 is rich, and λ > 1 is lean. The Equivalence Ratio (φ) is the inverse of Lambda (φ = 1/λ). Modern cars use oxygen sensors (Lambda sensors) to keep λ very close to 1.0 for the catalytic converter to work efficiently.