Enter the total mass of the air and the total mass of the fuel into the calculator to determine the air to fuel ratio.

Air to Fuel Ratio Formula

The following formula is used to calculate an air to fuel ratio:

AFR = Mair / Mfuel

  • Where AFR is the air to fuel ratio
  • Mair is the mass of the air
  • Mfuel is the mass of the fuel

What is an air to fuel ratio?

Air to fuel ratio is a measure of the total mass of the air per unit of mass of fuel used for an engine. Sometimes the air to fuel ratio can be calculated volumetrically, but this is uncommon.

Common Air to Fuel Ratios of Fossil Fuels

FuelAFR
Methanol6.47:1
Diesel 14.5:1
Propane 15.67:1
Gasoline 14.7:1
Hydrogen34.3:1
Methane17.19:1

How to calculate Air to Fuel ratio?

The following example outlines the steps needed to calculate an air to fuel ratio (AFR).

First, determine the mass of the air. This can be done by multiplying the volume of the air by the density. In this case, this yields a mass of 100kg.

Next, determine the mass of the fuel. Using the same method as the previous step the mass of the fuel is found to be 12 kg.

Finally, calculate the air to fuel ratio using the formula:

AFR = Mair / Mfuel

AFR = 100 / 12

AFR = 8.33 : 1