A gallon of milk weighs approximately 8.6 pounds (about 3.9 kilograms). This is slightly heavier than a gallon of water, which weighs about 8.34 pounds, due to the fat, protein, carbohydrates, and minerals present in milk that increase its density compared to water

. The weight can vary slightly depending on the type of milk (whole, skim, etc.), but 8.6 pounds is a commonly accepted average. For reference, a quart of milk weighs about 2.15 pounds, and a half-gallon weighs about 4.3 pounds