\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.