What does tCO₂e mean?
tCO₂e stands for tonnes of carbon dioxide equivalent. It is the common unit for greenhouse gas emissions: different gases are converted into the amount of CO₂ that would cause the same warming over a set period, usually 100 years, and then added up.
How the conversion works: global warming potential
Each gas has a global warming potential (GWP) relative to CO₂ (GWP = 1). One tonne of a gas with a GWP of 28 counts as 28 tCO₂e. GWP values come from the Intergovernmental Panel on Climate Change (IPCC) assessment reports and are revised over time, so reports state which set they use.
| Gas | GWP-100, IPCC AR4 (2007) | GWP-100, IPCC AR5 (2014) | GWP-100, IPCC AR6 (2021) |
|---|---|---|---|
| Carbon dioxide (CO₂) | 1 | 1 | 1 |
| Methane (CH₄) | 25 | 28 | 27.0 (non-fossil) / 29.8 (fossil) |
| Nitrous oxide (N₂O) | 298 | 265 | 273 |
| Sulphur hexafluoride (SF₆) | 22,800 | 23,500 | 24,300 |
Corporate inventories under the GHG Protocol cover the seven gases of the Kyoto Protocol: CO₂, CH₄, N₂O, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), SF₆ and nitrogen trifluoride (NF₃). A report that says "CO₂" rather than "CO₂e" may only count carbon dioxide.
Units you will see in reports
| Unit | Meaning | In tonnes |
|---|---|---|
| kgCO₂e | kilograms | 0.001 t |
| tCO₂e, t-CO₂, MT (metric ton) | tonnes (1,000 kg) | 1 t |
| ktCO₂e, Gg | thousand tonnes (gigagram) | 1,000 t |
| MtCO₂e, MMT, Tg | million tonnes (teragram) | 1,000,000 t |
| GtCO₂e | billion tonnes | 1,000,000,000 t |
Watch out for "MT": in many US and Indian reports it means metric ton (1 tonne), not megatonne. "MMT" means million metric tons. Some reports also use short tons (0.907 t). On polluer.com, large figures are shortened with K (thousand) and M (million), so "109.6K tCO₂e" means about 109,600 tonnes.
Intensity figures
Besides absolute totals, reports often give emission intensity: tCO₂e per million of revenue, per employee, per tonne of product or per MWh generated. Intensity can fall while absolute emissions rise, so check both.
Related: Scope 1, 2 and 3 explained · the 15 Scope 3 categories.
More guides
- Scope 1, 2 and 3 emissions explained
- The 15 Scope 3 categories
- Market-based vs location-based Scope 2 emissions
- How to find a company's sustainability report and emissions data
- Sustainability reporting frameworks explained
- Limited vs reasonable assurance of emissions data
Last reviewed: October 2026. Spotted an error? Tell us.