The emission factor describes the amount of emissions generated with the quantity of product or service produced. Emission factors are used to determine the carbon footprint.
Emission factors can be of many types. They may describe the use phase or life-cycle emissions, include only carbon dioxide emissions or all greenhouse gas emissions in CO2 equivalents, and may sometimes be average values or represent a specific period of time. For example, the emission factor for electricity generation is often expressed in g CO2/kWh and the emission factor for food in kg CO2eq./kg.
The emission factor of a product or service is often referred to as the carbon footprint. To be precise, this is only the case when the emission factor describes the amount of life cycle greenhouse gas emissions in terms of carbon dioxide equivalents.