{ Cal"i*ber, 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. qālib 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.

&fist; 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.

Variant
• Diameter of the bore of a firearm. In rifled firearm barrels the caliber is obtained by measuring between opposite lands. A caliber 0.45 revolver has a barrel with a land diameter 45/100 of an inch. The Metric equivalent is 11.43 millimeters.
  
• The diameter of round or cylindrical body, as of a bullet, a projectile, or a column.
  
• Unit of measure used to express the length of the bore of a weapon. The number of calibers is determined by dividing the length of the bore of the weapon, from the breech face of the tube to the muzzle, by the diameter of its bore. A gun tube the bore of which is 40 feet (480 inches) long and 12 inches in diameter is said to be 40 calibers long.
  
• Fig.: Capacity or compass of mind.
  
• obsolete: degree of importance or station in society