Emission factors
What an emission factor is and how to choose a suitable one.
Published on 10/08/2026
An emission factor converts an activity figure (a kilogram of steel, a kilowatt-hour, a kilometre of transport) into kilograms of CO2 equivalent (kgCO2e). The total of an emission is simply: the figure you entered multiplied by the factor.
What a factor carries
- a unit (kg, kWh, km, part): it must match the figure you are entering;
- a source: the recognised database it comes from;
- often a location: the Swiss electricity mix differs from the Chinese one, the same process does not have the same footprint everywhere;
- a value in kgCO2e per unit.
CO2 equivalent
All greenhouse gases are brought onto a single scale, CO2 equivalent, taking their warming potential into account. A kilogram of methane or refrigerant gas therefore weighs far more than a kilogram of CO2. You have nothing to calculate: the factor already includes this conversion.
How to choose well
- take the factor whose unit matches your figure exactly (do not enter kilograms against a per-kilometre factor);
- prefer the location closest to reality (Swiss electricity for a workshop in Geneva);
- choose the label most specific to the actual material or process (for example "stainless steel" rather than a generic steel);
- failing an exact factor, a reasonable proxy is acceptable, provided you document it (for example aluminium oxide as an approximation of sapphire).
Sources and uncertainty
The databases provided (for example BAFU for Switzerland, ADEME's Base Carbone) are built differently: some are in English, others in French, and values can vary from one database to another. Two useful habits:
- stay consistent in your choice of sources from one inventory to the next, so that your year-on-year comparisons keep their meaning;
- keep in mind that a factor remains an average: aiming for the right order of magnitude and the right source is worth more than chasing false precision down to the gram.
In the platform's factor search, filter by source and keyword, then keep the one whose unit and label best fit your entry.