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Definition

CO2 equivalent (CO2e) Definition

CO2 equivalent (CO2e) expresses different greenhouse gases in one unit by multiplying each gas's mass by its specified 100-year global warming potential, then adding the converted amounts.

What is CO2 equivalent (CO2e)?

CO2e is the common unit used to add greenhouse gases with different warming effects. A global warming potential (GWP) states the effect of one mass unit of a gas relative to CO2 over a specified time horizon. CO2 has a GWP of 1. Corporate inventories cover seven gas groups: CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride and nitrogen trifluoride.

Why does CO2 equivalent (CO2e) matter to you?

CDP 2026 full Questions 7.6 and 7.7, and SME Questions 20.4 and 20.5, ask for gross global Scope 1 and Scope 2 emissions in metric tons CO2e. Question 7.45 asks for combined Scope 1 and Scope 2 intensity in metric tons CO2e per unit of revenue. A CO2-only result cannot answer those fields if methane, nitrous oxide or refrigerant emissions are also within your boundary.

A customer may ask for your total in metric tonnes CO2e, the Scope 1, 2 and 3 split, reporting period, factor sources and calculation file. Use the same disclosed GWP table for the current inventory, the base-year inventory used to measure target progress, and each later progress calculation. Changing from one IPCC assessment report to another can change CO2e without any change in fuel, electricity or refrigerant use, so record and explain any recalculation.

How is CO2 equivalent (CO2e) calculated?

When gas masses are available separately, calculate each line as gas mass x that gas's 100-year GWP. Add the resulting kg CO2e, then divide by 1,000 once to report metric tonnes CO2e. Keep the gas name, mass unit, GWP value, time horizon and IPCC assessment report on the calculation line.

Many published emission factors already state kg CO2e per kWh, litre, kilometre or kilogram of refrigerant. In that case, multiply the activity by the factor and do not apply another GWP. A factor stated only as kg CO2 per unit covers carbon dioxide, not automatically all greenhouse gases. The unit on the source factor decides which calculation you have.

What mistakes should you avoid?

  • Relabelling a kg CO2 result as kg CO2e without checking whether the factor includes non-CO2 gases.
  • Multiplying by a GWP again when the published factor is already expressed in CO2e.
  • Mixing AR4, AR5 and AR6 GWP values in one inventory, or omitting the assessment report and 100-year time horizon from the method note.
  • Adding kilograms to tonnes, or dividing by 1,000 twice when converting kg CO2e to metric tonnes CO2e.

Is CO2e the same as CO2?

No. CO2 names one greenhouse gas. CO2e is a calculated unit that can include CO2 and non-CO2 gases after conversion. A factory line showing 10 tonnes CO2 says which gas was measured. A line showing 10 tonnes CO2e states the common-unit result but still needs the underlying gases or factor source.

Can you compare CO2e totals made with different GWP sets?

Not directly. First check the time horizon and IPCC assessment report behind each total. If they differ, recalculate the affected non-CO2 gases on the basis required for the comparison. Keep the original and recalculated versions so a reviewer can follow the change.

What do you send when a customer asks for CO2e?

Send the requested total and scope split with the reporting period and boundary. Include a calculation file showing each activity, gas or factor, value, unit, source year, geography, GWP basis and kg-to-tonne conversion. Keep invoices, meter exports, fuel logs and refrigerant service records behind those lines.

Worked example

Suppose a machinery maker in Germany records 420,000 kWh of purchased grid electricity and a measured release of 6 kg of HFC-134a refrigerant for one factory in 2026. For electricity, the Keslio factors dataset uses key grid_de_uba_2025_direct_thg at 0.352 kg CO2e/kWh. UBA's 2026 report identifies this as Germany's estimated 2025 direct greenhouse gas factor without upstream emissions. For HFC-134a, the dataset uses key refrigerant_hfc_134a_desnz_2026 at 1,300 kg CO2e/kg refrigerant from the UK DESNZ and DEFRA 2026 Government GHG Conversion Factors for Company Reporting.

Electricity: 420,000 kWh x 0.352 kg CO2e/kWh = 147,840 kg CO2e. Refrigerant: 6 kg x 1,300 kg CO2e/kg refrigerant = 7,800 kg CO2e.

Add the two results only after both are in kg CO2e: 147,840 + 7,800 = 155,640 kg CO2e. Divide by 1,000 once to report 155.64 metric tonnes CO2e for these two lines.

Both published factors already return CO2e, so the company does not apply another GWP. The result is not the factory's complete inventory because it includes only grid electricity and the measured refrigerant release.

Where you'll meet it

CDP 2026 gross global Scope 1 and Scope 2 emissions in metric tons CO2eCDP full Questions 7.6 and 7.7; SME Questions 20.4 and 20.5AASB S2 aggregation of seven greenhouse gases into metric tonnes CO2e using 100-year GWP valuesAASB S2 paragraph 29(a)(i), B20-B22 and AusB22.1ESRS E1-6 gross Scope 1, Scope 2, Scope 3 and total GHG emissions in metric tonnes CO2eqDelegated Regulation (EU) 2023/2772, ESRS E1 paragraph 44

Related terms

Global warming potential (GWP)

Global warming potential (GWP) is the multiplier that converts the mass of methane, nitrous oxide, refrigerants and other non-CO2 greenhouse gases into carbon dioxide equivalent over a stated time horizon.

Emission factor

An emission factor converts a measured activity, such as kilowatt-hours of electricity or litres of fuel, into greenhouse gas emissions by stating the emissions released per unit of that activity.

Scope 1 Emissions

Scope 1 emissions are greenhouse gases released directly from sources your company owns or controls, including fuel-burning equipment and vehicles, industrial processes, and refrigerant or other gas leaks.

Scope 2 Emissions

Scope 2 emissions are the indirect greenhouse gas emissions from generating the electricity, steam, heat, and cooling your company buys and uses.

Carbon Accounting

Carbon accounting is the process of defining a company’s greenhouse gas inventory, collecting activity data, applying emission factors, and reporting Scope 1, Scope 2, and Scope 3 emissions on a consistent basis.

Sources

  • Australian Accounting Standards Board

    CO2e definition; metric-tonne disclosure; seven-gas aggregation; 100-year GWP conversion; AR6 basis in paragraphs 29(a)(i), B20-B22 and AusB22.1

    2026-08-19

  • CDP

    Full Questions 7.6, 7.7 and 7.45 and SME Questions 20.4 and 20.5 use metric tons CO2e for emissions totals and intensity

    2026-08-19

  • German Environment Agency UBA

    The 2025 estimated direct GHG electricity factor without upstream emissions is 352 g CO2e/kWh, equivalent to 0.352 kg CO2e/kWh

    2026-08-19

Last verified 2026-08-19

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CO2 equivalent (CO2e) Definition | Keslio