Greenhouse Gas Calculator
Greenhouse gas inventories convert different gases into a single carbon dioxide equivalent (CO2e) so they can be compared and added. This calculator starts from an activity, such as fuel burned or electricity used, multiplies it by the emission factor you supply, and then weights methane and nitrous oxide by their global warming potentials before totalling everything in CO2e. Because emission factors and GWP values are empirical figures set by the EPA and the IPCC, every one is an editable input, so the result reflects the official standard you are required to use.
CO2 equivalent formula
CO2 from activity = activity * CO2 emission factor
Methane CO2e = CH4 mass * CH4 GWP
Nitrous oxide CO2e = N2O mass * N2O GWP
Total CO2e (kg) = CO2 + methane CO2e + nitrous oxide CO2e
Total CO2e (tonnes) = total kg / 1,000
Each gas mass is multiplied by its global warming potential to express it as the equivalent mass of carbon dioxide, then the equivalents are summed. One metric tonne equals 1,000 kilograms.
Greenhouse gas accounting context
- Global warming potential compares a gas to carbon dioxide over a time horizon, usually 100 years.
- The IPCC Fifth Assessment Report 100-year GWP values commonly used by the EPA are about 28 for methane and 265 for nitrous oxide.
- Emission factors depend on the fuel or electricity grid region and are published by the EPA.
- Carbon dioxide has a global warming potential of 1 by definition, so it needs no conversion.
- Always match the GWP set and emission factors to the reporting standard you are required to follow.
Greenhouse gas: frequently asked questions
What is CO2 equivalent (CO2e)?
CO2 equivalent expresses the warming effect of any greenhouse gas as the amount of carbon dioxide that would cause the same warming over a chosen time horizon. It is calculated by multiplying the mass of each gas by its global warming potential (GWP). This lets emissions of different gases be added on a single comparable scale.
What global warming potential values should I use?
Global warming potential values are published by the Intergovernmental Panel on Climate Change. The EPA and many inventories use 100-year GWP values such as 28 for methane and 265 for nitrous oxide from the IPCC Fifth Assessment Report. Because reporting programs differ, the GWP values in this calculator are editable so you can match your required standard.
What is an emission factor?
An emission factor is the quantity of a gas released per unit of activity, for example kilograms of CO2 per gallon of fuel burned or per kilowatt-hour of electricity. The EPA publishes emission factors for fuels and electricity. Enter the factor that matches your activity and the units you are using.
How do I total emissions from several gases?
Multiply each gas mass by its GWP to get its CO2 equivalent, then add the equivalents together. This calculator does that for carbon dioxide, methane, and nitrous oxide, the three most common gases in basic inventories, and reports a combined CO2e total.
Why are the emission factors and GWP values editable?
Emission factors and GWP values are empirical figures that depend on the fuel, the grid region, the standard, and the assessment year. To avoid shipping a number that could be wrong for your case, this calculator lets you enter the official values that apply to your activity from the EPA or IPCC.
Official sources
- U.S. Environmental Protection Agency: GHG Emission Factors Hub.
- U.S. EPA: Understanding Global Warming Potentials.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.