Caliber refers to the diameter of the bullet called bore. This can be measured in metric or standard For example a .45ACP in standard is 11.43x23 in metric.
9 millimeter is the caliber. IMPROVING ANSWER: A "9mm" bullet is actually .355 or .356 of an inch in diameter. So the caliber is about .36, but nobody calls it that because… it would be confusing. Everybody calls it a 9mm and if somebody asks you what "caliber" that pistol is, you can answer "It's a 9mm" without having to add or explain anything. further improve: 9mm is the correct answer. you can find the caliber by measuring the diameter of the bullet. translate to millimeters or inches and that's the caliber. 9mm is a 9mm caliber not "around .36" (MORE)
In a pure sense, it is a measure of the diameter of a bullet, usually given in decimal fractions of an inch (a .357 bullet is about.357 inches thick) In a broader sense, it is… the cartridge that a given weapon will fire- such as caliber .38 Special, or caliber 30-06. (MORE)
A ".45 caliber" can be a gun that uses .45 caliber ammunition or it can be a round of that ammunition. There are several specific calibers of small arms ammunition that are al…l generally called ".45 caliber." They have bullets that are roughly .454 of an inch or 454/1000 fractionally. A famous .45 caliber is the .45 Long Colt, invented in the 1870s and still popular today. It is used in revolvers. Another caliber that is the same diameter but a lot shorter in length is the .45 ACP or .45 automatic Colt pistol. It was made for use in the U.S. military's Model 1911 handgun, and it is still a popular caliber today in that gun and in other handguns. There are some rifles and carbines that use .45 caliber ammo, too. (MORE)
a .32 acp caliber pistol round is also called a 7.65mm in the metric designation. But that doesn't fit the real-world measurements, because a .32 pistol bullet is really more …like .30 or .31 caliber, and 7.8mm in metric measurements. The diameters of a 7.63 bullet and a .32 caliber bullet are similar, but that doesn't mean they're the same "caliber" or that they will fit the same guns. The 7.62 mm family of rifles are often called ".30 caliber" and they really are close to that, with the bullets either .308 or .311 diameter. (MORE)