Carbon Equivalent Calculator — CO₂e Converter
Select a greenhouse gas, enter its mass in kilograms, and convert it to CO₂ equivalent — the universal unit for comparing climate impact across different gases.
Greenhouse gas
kg
Equivalent warming impact as this mass of CO₂ over 100 years
- 1
GWP₁₀₀ factor
29.8Global warming potential relative to CO₂ over 100 years (IPCC AR6, 2022). - 2
CO₂ equivalent
100 × 29.8 = 2,980
How does this calculator work?
CO₂e (kg) = mass (kg) × GWP₁₀₀. Key IPCC AR6 (2022) values: CH₄ (fossil) = 29.8, N₂O = 273, HFC-134a = 1,526, SF₆ = 25,200. Multiply the gas mass by its GWP to find the warming impact expressed as an equivalent mass of CO₂. 100 kg of fossil methane equals 2,980 kg CO₂e.
Formula
How this is calculated
Different greenhouse gases trap heat with very different efficiencies. CO₂ is the reference gas (GWP = 1 by definition). To compare gases on equal footing, scientists use the Global Warming Potential (GWP) — the cumulative radiative forcing of 1 kg of a gas relative to 1 kg of CO₂ over a chosen time horizon. Multiplying the mass of any greenhouse gas by its GWP₁₀₀ converts it to CO₂ equivalent (CO₂e), expressed in the same kg unit.
The GWP values used here are from the IPCC Sixth Assessment Report (AR6, 2022): fossil methane 29.8, biogenic methane 27.9, nitrous oxide 273, HFC-134a 1,526, HFC-125 3,740, SF₆ 25,200 and NF₃ 17,400. Earlier reports (AR5, 2014) used slightly different figures (CH₄ = 28); many national greenhouse-gas inventory systems still cite AR5. If your context requires different GWP values, use the custom option.
The two context metrics — equivalent car kilometres and days of tree absorption — are indicative estimates using widely cited averages: 0.21 kg CO₂e per km for a European petrol passenger car (ICCT, 2022), and 21 kg CO₂ per year for an average mature broadleaf tree. They are rough reference points, not precise measurements, and vary widely with driving style, vehicle type and tree species.
Frequently asked questions
CO₂ is the specific molecule carbon dioxide. CO₂e (CO₂ equivalent) is a unit that expresses the combined climate impact of any greenhouse gas — or mix of gases — as the equivalent mass of CO₂. It allows all greenhouse gases to be added into a single comparable number for inventories and targets.
Methane absorbs infrared radiation far more efficiently per molecule than CO₂. Over 100 years its GWP is about 28–30 because it also oxidises to CO₂ in the atmosphere, adding further warming. Over 20 years (GWP₂₀) methane scores ~80, reflecting its intense but shorter-lived initial pulse.
Most national and corporate carbon inventories use GWP₁₀₀ (100-year), as specified in the UNFCCC reporting guidelines and the Paris Agreement frameworks. GWP₂₀ is used when near-term climate impacts are the priority (e.g., methane reduction pledges). This calculator uses GWP₁₀₀ by default; select Custom GWP to enter a 20-year or 500-year value instead.
TG we-Calculate Editorial Team. (2026). Carbon Equivalent Calculator — CO₂e Converter [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/carbon-equivalent-calculator
TG we-Calculate Editorial Team. "Carbon Equivalent Calculator — CO₂e Converter." TG we-Calculate. 2026. https://we-calculate.com/calculator/carbon-equivalent-calculator.
TG we-Calculate Editorial Team, "Carbon Equivalent Calculator — CO₂e Converter," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/carbon-equivalent-calculator
@misc{wecalculate_carbon_equivalent_calculator, title = {Carbon Equivalent Calculator — CO₂e Converter}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/carbon-equivalent-calculator}}, year = {2026}, note = {TG we-Calculate} }
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