Convert from royal foot to caliber

Unit Definition (royal foot)
The royal foot is a French pied de roi, also called the Paris foot in English.

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."