Greenhouse Gas Emission Factor Converter

An emission factor is a coefficient that converts activity data (e.g., kWh of electricity used, gallons of fuel burned) into greenhouse gas emissions. It is calculated as: Emissions = Activity Data × Emission Factor. For CO₂, the factor is based on the carbon content of the fuel multiplied by the oxidation fraction. For example, natural gas has an emission factor of 5.3 kg CO₂ per therm because each therm contains approximately 14.4 kg of carbon that is almost completely oxidized during combustion. Emission factors vary by fuel type, combustion technology, and regional grid mix.

GWP measures how much energy 1 kg of a greenhouse gas absorbs over a specific time period compared to 1 kg of CO₂. CO₂ has a GWP of 1 by definition. The 100-year GWP (GWP100) is most commonly used for reporting under the UNFCCC. However, short-lived gases like methane have much higher GWP20 values (81 vs 27 at GWP100) because they are potent but decay quickly. Long-lived gases like SF₆ maintain their potency for millennia. The choice of time horizon significantly affects the relative importance of different gases in carbon equivalence calculations.

To convert methane (CH₄) emissions to CO₂ equivalent (CO₂e), multiply the mass of CH₄ by its GWP value. Using IPCC AR6 values: CO₂e = Mass of CH₄ × 27 (GWP100) or CO₂e = Mass of CH₄ × 81 (GWP20). For example, 1 kg of methane = 27 kg CO₂e over 100 years. This means methane is 27 times more potent than CO₂ over a century, but 81 times more potent over 20 years. This conversion is essential for calculating an organization's carbon footprint across all emission sources.

Direct emission factors apply to sources you directly control, like burning natural gas in a furnace (5.3 kg CO₂/therm) or driving a gasoline vehicle (8.887 kg CO₂/gallon). Indirect emission factors apply to purchased energy like electricity, where the emissions occur at the power plant but are attributed to the consumer. The average US grid emission factor is 0.42 kg CO₂/kWh, but this varies by region from 0.3 (renewable-heavy grids) to 0.9 (coal-heavy grids). Location-based factors use regional grid mix averages while market-based factors use purchased energy certificates.