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 diameter of the inside of a round cylinder, such as a tube.
- The diameter of the bore of a firearm, usually shown in hundredths or thousandths of an inch and expressed in writing or print in terms of a decimal fraction: .45 caliber.
- The diameter of a large projectile, such as an artillery shell, measured in millimeters or in inches.
- Degree of worth; quality: a school of high caliber; an executive of low caliber.