Emission factor
An emission factor is a representative ratio that relates the quantity of a pollutant or greenhouse gas released to a unit of activity, material, fuel, energy, output, or distance. It converts measured activity data into an estimated emission quantity when direct measurement is unavailable or impractical.
In simple terms
A calculation commonly multiplies activity data by an applicable factor: litres of fuel by emissions per litre, for example. Factors may be technology-specific, supplier-specific, regional, national, or generic, and may cover one gas or a carbon dioxide equivalent total. Their units, geographic fit, year, system boundary, heating-value basis, and global warming potential source must match the calculation. More specific data are not automatically better unless they are reliable and appropriate.
Why it matters
Emission factors are fundamental inputs to carbon accounting and greenhouse gas inventories, including many Scope 1, Scope 2, and Scope 3 estimates. Selecting an unsuitable or outdated factor can distort the result. Recording the factor source and version makes calculations reproducible and helps explain changes when datasets are revised.
Example
For example, a fleet manager can multiply litres of diesel consumed by a documented fuel-combustion factor with compatible units. If the factor reports individual gases, the calculation may apply the selected global warming potential values before expressing the combined result in carbon dioxide equivalent.
How it differs
Carbon accounting
An emission factor is a ratio used in a calculation; carbon accounting is the wider method that sets boundaries, gathers data, applies factors or measurements, and reports the resulting emissions.