Fuel Combustion Emission Calculator
Greenhouse gas inventories calculate combustion emissions with a simple identity: emissions equal the quantity of fuel burned (the activity data) multiplied by an emission factor for that fuel. The emission factor is the mass of carbon dioxide released per unit of fuel, such as kilograms of CO2 per gallon, per litre, or per therm. This calculator multiplies your fuel quantity by the official emission factor you supply, then lets you apply a global warming potential to express the result in carbon dioxide equivalent. Because the correct factor depends on the exact fuel and unit, it is a user-editable input you can fill from a published source such as the EPA Emission Factors Hub.
Combustion emission formula
Emissions (kg CO2) = fuel quantity * emission factor
Emissions (tonnes CO2) = emissions kg / 1,000
Emissions (kg CO2e) = emissions kg CO2 * GWP factor
Emissions (tonnes CO2e) = emissions kg CO2e / 1,000
Keep the fuel quantity and emission factor in matching units. The GWP factor is 1 for pure CO2; use a higher value only if your factor bundles other gases.
Emission factor context
- Emissions equal activity data times an emission factor, the core inventory identity.
- Fuel-based CO2 factors assume the fuel carbon is fully oxidised on combustion.
- The EPA Emission Factors Hub publishes factors for many stationary and mobile fuels.
- Global warming potential converts methane and nitrous oxide to CO2-equivalent terms.
- Activity data and emission factor must use the same unit; this tool does not convert units.
Fuel emissions: frequently asked questions
How are fuel combustion emissions calculated?
Emissions equal the quantity of fuel burned times an emission factor for that fuel: emissions = activity data times emission factor. The emission factor is the mass of carbon dioxide released per unit of fuel, for example kilograms of CO2 per gallon, per litre, or per therm. Multiply, then optionally apply a global warming potential to combine gases.
Where do emission factors come from?
Published emission factors for stationary and mobile combustion are issued by bodies such as the U.S. EPA in its Emission Factors Hub. Because the right factor depends on the exact fuel and unit you are using, this calculator takes the emission factor as a user-editable input so you can paste in the official value for your fuel.
What is CO2e?
Carbon dioxide equivalent (CO2e) expresses the warming effect of all greenhouse gases on a common scale by multiplying each gas by its global warming potential (GWP). For pure CO2 the GWP is 1. Enter a GWP factor to fold in methane or nitrous oxide if your emission factor already covers those gases.
Does combustion efficiency change the result?
Standard fuel-based emission factors assume complete combustion of the carbon in the fuel, so the CO2 figure depends mainly on how much fuel is burned, not on appliance efficiency. Efficiency affects how much useful work you get per unit of fuel, which is a separate calculation.
Can I use any unit?
Yes, as long as your fuel quantity and emission factor share the same unit basis. If your factor is kilograms of CO2 per gallon, enter the fuel in gallons. The calculator does not convert units, so keep the activity data and factor consistent.
Official sources
- U.S. Environmental Protection Agency: GHG Emission Factors Hub.
- U.S. Environmental Protection Agency: Understanding Global Warming Potentials.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.