CO2 g/km

A car's official carbon dioxide emissions per kilometer, measured on the WLTP cycle in the EU and UK. Many taxes and incentives key off this number.

Last reviewed

CO2 g/km states how many grams of carbon dioxide a car emits per kilometer under its official test, WLTP in the EU and UK. Since CO2 output is tied directly to fuel burned, the figure moves in lockstep with fuel consumption: an efficient small gas car emits far less per kilometer than a heavy SUV, and a BEV is rated at zero g/km because no tailpipe emissions are measured.

The number matters to your wallet. UK company car tax (BiK) percentages are keyed to it, UK Vehicle Excise Duty in a car's first year depends on it (GOV.UK lists zero-emission cars at the lowest first-year rate), and France's CO2 malus at first registration follows a scale on it. Two similar cars can carry different tax bills because one emits slightly more.

For plug-in hybrids, a low official CO2 figure assumes a share of driving on electricity, so it holds only if you plug in regularly. Check the charge-sustaining consumption too.

Differs by market

UK and French taxation scales with CO2 g/km: examples include the UK's BiK company car tax bands and France's CO2 malus. The US instead publishes greenhouse gas ratings through the EPA label.

  1. Vehicle Certification Agency, The Worldwide Harmonised Light Vehicle Test Procedure (WLTP)
    UK Vehicle Certification Agency Accessed
  2. European Environment Agency, CO2 emissions performance of new passenger cars in Europe
    European Environment Agency Accessed
  3. Service-Public.fr, Tax on CO2 emissions from passenger vehicles (CO2 malus)
    Service-Public.fr (French government) Accessed
  4. GOV.UK, Vehicle tax rate tables
    GOV.UK Accessed
  5. GOV.UK, Taxation of company cars: the appropriate percentage for 2025 to 2028
    HM Revenue & Customs Accessed
  6. fueleconomy.gov, Learn more about the gasoline vehicle label
    US EPA and DOE Accessed

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