tCO₂e stands for tonnes of carbon dioxide equivalent. It is the unit used in virtually every credible greenhouse gas (GHG) report, including those produced under the GHG Protocol, ISO 14064, PPN 006 Carbon Reduction Plans, and the UK's Streamlined Energy and Carbon Reporting (SECR) regime.
Greenhouse gases other than CO₂ — methane (CH₄), nitrous oxide (N₂O), refrigerant gases, and others — trap heat at very different rates. Methane, for example, is roughly 25 times more potent than CO₂ over a 100-year period; some refrigerants are thousands of times more potent. To compare emissions across gases on a single scale, every gas is multiplied by its Global Warming Potential (GWP) and expressed as the equivalent quantity of CO₂.
Why it matters
Without a common unit, you cannot meaningfully add up emissions from different sources, compare year-on-year performance, or report against a target. A diesel van, a leaking air-conditioning unit, and a tonne of food waste all release different gases — but expressed in tCO₂e, they sit on the same scale and can be aggregated into a single footprint figure.
Procurement frameworks (PPN 006, NHS Net Zero Supplier Roadmap), tender questionnaires (EcoVadis, CDP), and sustainability disclosures (SECR, CSRD) all expect emissions to be reported in tCO₂e.
A practical example
If your business releases 10 kg of methane through a refrigerant leak, that is equivalent to roughly 250 kg (0.25 tonnes) of CO₂ in terms of warming impact — expressed as 0.25 tCO₂e. Add that to, say, 5 tCO₂e from your gas boiler and 12 tCO₂e from your fleet diesel, and the total footprint for those sources is 17.25 tCO₂e.
We use tCO₂e on every page of every Carbon Impact Report we produce. See where it appears in our process on the methodology page.