On average, a gallon of milk weighs approximately 8.6 pounds. This weight can vary depending on the amount of fat in the milk. Milk that contains a higher fat content weighs more than skim milk, for example.
In an effort to provide healthier substitutes for traditional whole milk, some milk producers skim a portion of the fatty content before packaging it as low-fat or 2 percent milk. This removed portion is sometimes used to make milk by-products like cheese and cream. Because of the missing fat, and the fact that milk is approximately 87 percent water, skim milk generally has a thinner consistency and a more watery taste.