Question: 20 gauge is what caliber?
Answer: The 20-gauge shotgun, also known as "20 bore", is a type of smooth-bore shotgun that fires a shell that is smaller in caliber (. 615 in (15.6 mm)) than a 12 gauge shotgun (. 729 in (18.5 mm)). It is often used by beginning shooters for target practice and for hunting small game.