Convert from inch [international, U.S.] to caliber

Unit Definition (inch [international, U.S.])
The inch is a traditional measurement of distance equal to 1/12 of a foot, or exactly 2.54 centimeters. The Old English word "ynce" is derived from the Latin uncia, meaning a 1/12 part. It follows that "inch" and "ounce" actually have the same origin. The inch was originally defined in England in two ways: as the length of three barleycorns laid end to end, or as the width of a man's thumb at the base of the nail. The barleycorn definition is peculiarly English, but the thumb-width definition is generic. In many european languages the word for inch actually also means thumb: examples include the Dutch duim, Swedish tum, French pouce, and Spanish pulgada. In the history of English units the inch seems to come before the foot, as after the Norman conquest of 1066, the foot was defined as 12 inches, rather than the inch being defined as 1/12 foot.

Unit Definition (caliber)
The caliber is a unit used to express the bore diameter of a gun. Traditionally, the diameter is stated in inches, so that ".22 caliber" refers to a pistol having a bore of 0.22 inches (5.588 mm). So the caliber is actually equivalent to the inch. The usage of the term "caliber" is actually now in decline, because bore diameters of many guns are now stated in millimeters. "Caliber" is the American spelling; elsewhere the unit is often spelled "calibre."