AFR Calculator - Air-Fuel Ratio, Lambda and Equivalence Ratio

Your details

Mass mode: enter how much air and fuel you measured. Fuel preset mode: pick a fuel, and enter the actual AFR from your sensor or dyno sheet to compute lambda and percent excess air.
Total mass of air entering the combustion chamber (any unit, as long as both are the same).
g
Total mass of fuel. Use the same unit as mass of air.
g
Air-Fuel Ratio (AFR)Stoichiometric
14.7

Mass of air per unit mass of fuel

Stoichiometric AFR14.7
Lambda (lambda)1
Equivalence Ratio (phi)1
Excess Air0%
MixtureStoichiometric
1 lambda
Very Rich<0.8Rich0.8-0.95Stoichiometric0.95-1.05Lean1.05-1.2Very Lean1.2+

AFR 14.700 is exactly stoichiometric for the reference fuel (gasoline).

  • The stoichiometric AFR for the reference fuel (gasoline) is 14.70:1 - the ratio that burns all fuel with no leftover oxygen.
  • Equivalence ratio (phi) is 1.000 (phi = 1/lambda). Values above 1 indicate rich, values below 1 indicate lean.
  • The mixture is at exactly stoichiometric - ideal for catalytic converter efficiency.
  • Lambda 1.0 maximizes catalytic converter efficiency. Racing engines often target lambda 0.85-0.92 (rich) for power, while lean-burn engines aim for lambda 1.1-1.4 for economy.

Next stepUse lambda as a tuning target alongside exhaust gas temperature (EGT) and power output for optimal calibration.

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