Calculate air-fuel ratio from air and fuel mass, or find lambda and equivalence ratio from actual and stoichiometric AFR with fuel presets.

Ratios use mass, not volume. Presets are approximate; E85 and natural gas vary by composition. Verify the actual fuel. This is not an engine tuning recommendation.

Related Calculators

Lambda Air/Fuel Ratio Formula

The following formula is used to calculate the lambda air/fuel ratio for a given actual and stoichiometric air/fuel ratio.

ฮป = (AFRactual) / (AFRstoich)

Variables:

  • ฮป is the lambda value
  • AFRactual is the actual air/fuel ratio
  • AFRstoich is the stoichiometric air/fuel ratio

To calculate the lambda value, divide the actual air/fuel ratio by the stoichiometric air/fuel ratio.

What is a Lambda Air/Fuel Ratio?

The lambda air/fuel ratio is a measure of the air-to-fuel mixture in an internal combustion engine. It is used to determine whether the engine is running lean (too much air) or rich (too much fuel). A lambda value of 1 indicates the theoretical stoichiometric mixture for the fuel reference; it does not guarantee complete combustion or safe engine operation. Values less than 1 indicate a rich mixture, while values greater than 1 indicate a lean mixture. Monitoring and adjusting the lambda value is crucial for optimizing engine performance, fuel efficiency, and emissions.

How to Calculate Lambda Air/Fuel Ratio?

The following steps outline how to calculate the Lambda Air/Fuel Ratio.

  1. First, determine the actual air/fuel ratio (AFRactual).
  2. Next, determine the stoichiometric air/fuel mass ratio (AFRstoich) for the actual fuel. The default 14.7 gasoline reference and fuel suggestions are approximate; ethanol blend composition can vary.
  3. Finally, calculate the lambda value using the formula ฮป = AFRactual / AFRstoich.
  4. Select Lambda, enter the actual and stoichiometric mass ratios, and select Calculate. The calculator also provides mass-based AFR and inverse solves; equivalence ratio ฯ† is 1/ฮป.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Actual Air/Fuel Ratio (AFRactual) = 14.7

Stoichiometric Air/Fuel Ratio (AFRstoich) = 14.7