An emission factor (EF) measures the emissions associated with one additional unit of a specified activity. For example, it could be the extra emissions associated with spending one euro on clothing or transportation. It could also be the extra emissions associated with purchasing one kilogram of textile or one liter of fuel.

If a company reports how much it has spent on various products and services, spend-based EFs allow us to estimate the company’s emissions. If a company more specifically reports the quantities of all purchased items, activity-based EFs provide an even more accurate estimate of the company’s emissions.