What is "a ship's caliber"

Caliber \Cal"i*ber\, Calibre \Cal"ibre\, n. [F. calibre, perh. fr. L. qualibra of what pound, of what weight; hence, of what size, applied first to a ball or bullet; cf. also Ar. q[=a]lib model, mold. Cf. Calipers, Calivere.]

1. (Gunnery) The diameter of the bore, as a cannon or other firearm, or of any tube; or the weight or size of the projectile which a firearm will carry; as, an 8 inch gun, a 12-pounder, a 44 caliber.

   The caliber of empty tubes.
   --Reid.

   A battery composed of three guns of small caliber.
   --Prescott.

   Note: The caliber of firearms is expressed in various ways. Cannon are often designated by the weight of a solid spherical shot that will fit the bore; as, a 12-pounder; pieces of ordnance that project shell or hollow shot are designated by the diameter of their bore; as, a 12 inch mortar or a 14 inch shell gun; small arms are designated by hundredths of an inch expressed decimally; as, a rifle of .44 inch caliber.

2. The diameter of round or cylindrical body, as of a bullet or column.

3. Fig.: Capacity or compass of mind.
   --Burke.

   Caliber compasses. See Calipers.

   Caliber rule, a gunner's calipers, an instrument having two scales arranged to determine a ball's weight from its diameter, and conversely.

   A ship's caliber, the weight of her armament.