There are 4 main sizes of commercial kegs that are used regularly. Sixth Barrel, Short/Quarter Barrel (AKA Pony Keg), Slim/Quarter Barrel, and the Half Barrel. 1  Sixth Barrel (23.3″x9.25″D) | 55 -12oz.  Short/Quarter Barrel (14.8″x16.125″D) | 82 -12oz.