Equivalence Ratio Calculator

Equivalence Ratio Calculator: Characterize Mixture Richness

Equivalence ratio (phi) is the standard dimensionless way combustion engineers describe how far a fuel-air mixture deviates from the ideal stoichiometric ratio, independent of the specific fuel or air quantities involved.

The Formula

Phi = Stoichiometric AFR / Actual AFR

Worked Example

A mixture has an actual AFR of 16:1 against a stoichiometric AFR of 14.7:1.

Phi = 14.7 / 16 = 0.92 (a lean mixture)

How to Use This Calculator

1. Enter the actual air-fuel ratio the system is running.
2. Enter the stoichiometric air-fuel ratio for the fuel in use.
3. Click Calculate to get the equivalence ratio and mixture classification.

Related Calculations

Compare with the Lambda Calculator, the reciprocal convention used in automotive combustion control.