Free AFR Calculator
Use this Free AFR Calculator to work through the same calculation as the main calculator page with clear steps, examples, and result context.
--
Run the calculator.
What This Free AFR Calculator Helps You Do
This page translates the basic air-fuel mass relationship into whichever number you are missing. That makes it useful for classroom combustion problems, calibration planning, and quick sanity checks on airflow or fueling assumptions.
It also reports lambda relative to a stoichiometric reference so the result is easier to interpret as rich, stoich, or lean instead of just reading a raw ratio.
How to Calculate Free AFR Calculator
- Choose the AFR task: Solve for the ratio directly or for the fuel or air mass needed to hit a target ratio.
- Use consistent mass units: Air and fuel can be grams, kilograms, or pounds as long as both use the same unit.
- Set the target AFR: Stoichiometric gasoline is often referenced near 14.7:1, but tuning targets vary by fuel and engine state.
- Review lambda: Lambda compares the calculated AFR with the stoichiometric reference and helps classify rich versus lean operation.
Free AFR Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| AFR | Air-fuel ratio by mass | ratio |
| Air mass | Mass of air entering combustion | g, kg, lb, or any consistent mass unit |
| Fuel mass | Mass of fuel used for combustion | same mass unit as air |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- Air mass: 147 g
- Fuel mass: 10 g
Result: 147 / 10 = 14.7:1.
This is the classic stoichiometric gasoline reference ratio by mass.
- Air mass: 294 g
- Target AFR: 14.7
Result: Fuel mass = 294 / 14.7 = 20 g.
Target-ratio calculations help convert airflow information into a matching fuel requirement.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Lambda below 1 | The mixture is richer than the stoichiometric reference. | Useful for power or cooling in some setups, but check emissions and washdown risk. |
| Lambda near 1 | The mixture is close to the stoichiometric reference. | This is a common control target for catalytic-converter operation. |
| Lambda above 1 | The mixture is leaner than the stoichiometric reference. | Check combustion stability and component temperatures. |
Frequently Asked Questions
References
Last reviewed: March 2026