AFR ↔ Lambda calculator
Convert air-fuel ratio to lambda (and equivalence ratio φ) for any fuel.
Lambda is fuel-independent (λ 1.0 = stoich for any fuel), which is why tuners target lambda. Commanded ≠ delivered — verify with a wideband before boost.
How AFR and lambda relate
AFR is the mass ratio of air to fuel. Lambda normalizes that to the fuel's stoichiometric point, so lambda 1.0 is stoichiometric for any fuel — that's why tuners target lambda, especially on flex-fuel. Pump gas is ~14.7:1 at stoich; E85 is ~9.8:1, so the same lambda 0.85 is a much lower AFR number on E85. Equivalence ratio φ is simply 1/lambda.
Typical WOT targets are roughly lambda 0.85–0.88 (about 12.5–13.0 AFR on gas) naturally aspirated, and richer (lambda 0.78–0.82) under boost. These are starting points — commanded is not delivered, so verify with a wideband before you trust them.