Keg sizes are not standardized from country to country or brewery to brewery; however, a standard keg in the United States is equal to a half barrel, or 15.5 gallons, of beer. Therefore a standard U.S. keg contains 165 12-ounce servings and 124 16-ounce servings.
Another frequently used type of keg in the United States is the "pony keg," which is equal to one-fourth barrel or 7.75 gallons. Some breweries also make "mini kegs" which are typically 5-liter kegs and are not refillable. Kegs are usually made out of stainless steel or aluminum. To dispense beer, a keg must be upright with the opening on the top.