The average fat, percentage in cow milk is about

The average fat, percentage in cow milk is about 4.2%.
The fat content of milk is the proportion of milk, by weight,   made up of butterfat. The fat content, particularly of cow's milk, is modified to make a variety of products.
The fat content of the raw milk produced by cows ranges from about 3.3% up to 5%. It varies by breed, and by diet, and can also be altered by selective breeding and genetic modification.