Air-Fuel Ratio Calculator
Calculate air-fuel ratio (AFR), lambda, and equivalence ratio for gasoline, E85, diesel, and other fuels.
How It Works
Enter air mass flow and fuel mass flow, or enter your target AFR and fuel type. The calculator computes lambda and equivalence ratio, and indicates whether the mixture is rich, lean, or stoichiometric.
Formula
Lambda = Actual AFR / Stoichiometric AFR
Frequently Asked Questions
What is stoichiometric AFR?
Stoichiometric AFR is the ideal air-to-fuel ratio for complete combustion with no excess air or fuel. For gasoline it is 14.7:1, for E85 it is approximately 9.76:1, and for diesel it is 14.5:1.
What AFR should I run at wide-open throttle?
For maximum power on gasoline, most turbocharged engines run 11.5:1 to 12.5:1 AFR (rich). Naturally aspirated engines typically peak at 12.5:1 to 13.2:1. Leaner mixtures burn hotter and risk detonation.