How to Use the Air-Fuel Ratio (AFR) Calculator
Calculate combustion stoichiometry and Lambda value step-by-step:
Select Fuel Type
Choose fuel (Gasoline 14.7, E85 9.8, Diesel 14.5, Methanol 6.4).
Enter Air Mass
Input measured or calculated intake air mass in kg or grams.
Enter Fuel Mass
Input injected fuel mass in matching weight units.
Evaluate Lambda
Get instant Lambda ratio λ and rich/lean condition assessment.
Key Features & Combustion Dynamics
Multi-Fuel Stoichiometry
Includes exact stoichiometric constants for 7 commercial and racing fuels.
Lambda Equivalent Calculation
Universal λ index for wideband oxygen sensor tuning.
Rich vs Lean Diagnostics
Evaluates power rich (0.85-0.90 λ) and fuel economy lean conditions.
Combustion Chemistry Guide: Air-Fuel Ratios & Lambda
The Air-Fuel Ratio (AFR) represents the mass ratio of air to fuel present in a combustion process. Complete stoichiometric combustion occurs when oxygen in the air reacts perfectly with hydrocarbon fuel molecules without leaving excess unburned fuel or unreacted oxygen.
Because stoichiometric ratios vary by fuel type (14.7 for gasoline vs 9.8 for E85), engine tuners utilize Lambda (λ), defined as:λ = Actual AFR / Stoichiometric AFRLambda allows universal tuning across different fuel blends independent of fuel energy density.
Frequently Asked Questions
?What is the best AFR for maximum power in gasoline engines?
For naturally aspirated gasoline engines, peak horsepower is typically produced at a rich AFR of ~12.5:1 to 12.8:1 (λ = 0.85 - 0.87).