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

Unit Definition (feet [international, U.S.])
The human foot has long been a standard unit for the measurement of length. Over history this size has varied from region to region and there is some discrepancy as to an exact standard or origin of the standard measurement for feet that we use today. In England, the Roman foot was replaced after the fall of Rome by the natural foot. The modern foot (1/3 yard or about 30.48 centimeters) did not appear until after the Norman conquest of 1066. It may be an innovation of Henry I, who reigned from 1100 to 1135. Later in the 1100's a foot of modern length, the "foot of St. Paul's," was inscribed on the base of a column of St. Paul's Church in London.

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."