What is an emission factor?

An emission factor is the multiplier used in most carbon accounting: activity data × emission factor = estimated emissions. For example, an emission factor for grid electricity (expressed in kg CO2e per kWh) lets a company convert its electricity bill into an estimate of the associated emissions.

Where emission factors come from

Emission factors are published by governments, industry bodies, and standards organizations — such as national grid emission factors, or factors published under the GHG Protocol. They vary by activity type, region, fuel source, and technology, since the same activity can produce very different emissions depending on context (grid electricity mix, for instance, varies significantly by country).

Why emission factor accuracy matters

Choosing the right emission factor — matched to the correct region, year, and activity type — is one of the most common sources of error in Scope 1, 2, and 3 emissions calculations. Using an outdated or generic factor instead of a location- or supplier-specific one can materially over- or understate a company's actual footprint.

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