To make butter, about 20-25 liters of milk are needed^{1 2} with 80-85% of the CO2e emissions coming from the raw milk production. The large variation in CO2e estimations for butter are a result of different ways in which the CO2e of milk is allocated according to fat and protein content.

For example, in Flysjö 2011³, a ratio of 1:1.7 is used between fat and protein content to allocate emissions based on market value⁴. This means that only ~40% of the CO2e of the milk are allocated to the butter in this study, as butter is typically 80% fat and 4% protein. The rest of the emissions are then allocated to other milk products high in protein such as buttermilk. For Flysjö 2011, this leads to about 9 kg CO2e / kg of butter, while other studies report values well over 20 kg CO2e / kg.