The fat content of milk is the proportion of milk, by weight,^[1]: 266 made up by butterfat. The fat content, particularly of cow's milk, is modified to make a variety of products. The fat content of milk is usually stated on the container, and the color of the label or milk bottle top varied to enable quick recognition.

‘Whole’ or ‘full-fat’ milk has more nutritional energy by volume than low fat milk, and researchers found that in general low fat milk drinkers do absorb less fat, but will compensate for the energy deficit by eating more carbohydrates. They also found that the lower fat milk drinkers also ate more fruits and vegetables, while the higher fat milk drinkers also ate more meat and sweets.^[2]

Nutrition intake between whole milk drinkers and skimmed or low fat drinkers is different. An analysis of a survey done by the U. S. Department of Agriculture showed that consumers of reduced or low fat milk had greater intake of vitamins, minerals, and dietary fiber compared to the group of whole milk drinkers, yet zinc, vitamin E, and calcium were all under consumed in each group. The conclusion was that the whole milk drinkers were more likely to choose foods that were less micronutrient-dense, which resulted in their less healthful diets.^[3]

Researchers at the University of Copenhagen, in Denmark, found that drinking full-fat milk may actually be better for your heart than drinking skimmed milk. This is because it boosted levels of HDL cholesterol in the bloodstream.^[4]

Today, most skim milk is created by spinning whole milk in a centrifuge so that the fat droplets separate out.^[5] To make low fat milk, one can simply mix skim and whole milk in a fixed ratio.^[6]

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. For example, scientists in New Zealand have bred cows that produce milk with less than 1% fat content.^[7]

Milk's fat content can be determined by experimental means, such as the Babcock test or Gerber method. Before the Babcock test was created, dishonest milk dealers could adulterate milk to falsely indicate a higher fat content. In 1911, the American Dairy Science Association's Committee on Official Methods of Testing Milk and Cream for Butterfat met in Washington DC with the U.S. Bureau of Dairying, the U.S. Bureau of Standards and manufacturers of glassware.^[8] Standard specifications for the Babcock methodology and equipment were published as a result of this meeting.^[9] Improvements to the Babcock test have continued.^[10][11]

The terminology for different types of milk, and the regulations regarding labelling, varies by country and region.

• Milk
• Milk powder
• Butterfat
• Cream