The number of people that a keg can serve depends on the serving size and the number of servings per person. Assuming that one person will have three servings of 12 ounces each, one keg of beer can serve 55 people.
A standard keg contains 15.5 U.S. gallons, which yields 165 12-ounce servings or 124 16-ounce servings. Other keg sizes are also available. The 1/4 keg, also known as the pony keg, contains 7.75 gallons and serves 82 12-ounce or 62 16-ounce beer. The 1/6 keg contains 5.16 gallons and serves 56 12-ounce or 42 16-ounce beers. Using this information, the size and number of kegs needed to serve a specific number of people can be estimated.