The term that describes the size of a rifle or handgun bore, as well as the size of cartridges used with different bores, is caliber. Caliber usually refers to the diameter of the bore measured from land to opposite land in rifled barrels and is expressed in hundredths or thousandths of an inch or in millimeters. For example, a .270 caliber rifle bore measures 0.270 inches in diameter. This term also applies to the size of the cartridges designed for those bores
. In summary, caliber is the standard term used to denote both the bore diameter of firearms and the size of the ammunition they use.
