Chemistry

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Air-Fuel Ratio Calculator.

Calculate air-to-fuel mass ratio and lambda from explicit masses.

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01

Set your values

Results update as you type.

Air-fuel ratio: 14.7

Air-fuel ratio

14.700000
Lambda: 1

Lambda

1.000000

Educational formula calculator. Keep units consistent; chemistry procedures, concentrations, and safety decisions require qualified laboratory guidance. Never mix cleaning products.

Use Cases

Tuning an engine for performance

Determine the current air-fuel ratio and lambda to adjust fuel delivery for optimal combustion and power.

Example: If you measure 12 kg of air and 1 kg of fuel, AFR is 12:1. With a stoichiometric AFR of 14.7, lambda is 0.816 (rich).

Checking fuel mixture in a lab or workshop

Quickly verify the air-fuel mixture of a combustion process by entering measured masses.

Example: For a test run with 20 g of air and 1.5 g of fuel, AFR is 13.33:1.

Frequently Asked Questions

What does the Air-Fuel Ratio Calculator do?
It calculates the air-to-fuel mass ratio (AFR) by dividing the air mass by the fuel mass. It also computes lambda, which is the actual AFR divided by the stoichiometric AFR you provide.
How is lambda calculated?
Lambda is the ratio of the actual air-fuel ratio to the stoichiometric air-fuel ratio. Lambda = (Air mass / Fuel mass) / Stoichiometric AFR. A lambda of 1 means stoichiometric, less than 1 is rich, greater than 1 is lean.
What units should I use for air and fuel mass?
You can use any consistent mass units (e.g., kg, g, lb) for both air and fuel. The calculator computes the ratio, so the units cancel out. Ensure both masses are in the same unit.

Tips & Common Mistakes

Tips

  • Ensure both air and fuel masses are in the same unit (e.g., kg, g, lb) to get an accurate ratio.
  • Know your fuel's stoichiometric AFR: gasoline ~14.7:1, diesel ~14.5:1, ethanol ~9:1.
  • Use lambda to compare mixtures across different fuels: lambda = 1 is stoichiometric, <1 is rich, >1 is lean.
  • For precise results, measure masses accurately and consider temperature and pressure effects on air density.

Common Mistakes to Avoid

  • Mixing units for air and fuel (e.g., kg for air and g for fuel) without converting, leading to incorrect AFR.
  • Using the wrong stoichiometric AFR for the fuel type, which skews lambda calculations.
  • Forgetting that lambda is a ratio of ratios, not a direct mass ratio.

Last updated: August 13, 2026