1. The diameter of a body; as the caliber of a column, or of a bullet.

2. The bore of a gun, or the extent of its bore.

Caliber-compasses, calibers, or callipers, a sort of compasses made with arched legs to take the diameter of round bodies, as masts, shot, &c. The legs move on an arch of brass, on which are marked the inches and half inches, to show how far the points of the compasses are opened asunder.

Caliber-rule, Gunners Callipers, an instrument in which a right line is so divided as that the first part being equal to the diameter of an iron or leaden ball of one pound weight, the other parts are to the first as the diameters of balls of two, three, four, &c. Pounds, are to the diameter of a ball of one pound. It is used by engineers, to determine, from a balls weight, its diameter or caliber and vice versa.