{"id":4363,"date":"2019-08-15T14:46:13","date_gmt":"2019-08-15T14:46:13","guid":{"rendered":"https:\/\/www.ammunitiontogo.com\/lodge\/?p=4363"},"modified":"2025-10-01T20:57:29","modified_gmt":"2025-10-01T20:57:29","slug":"what-is-caliber","status":"publish","type":"post","link":"https:\/\/www.ammunitiontogo.com\/lodge\/what-is-caliber\/","title":{"rendered":"What is Caliber?"},"content":{"rendered":"

Understanding the world of firearms often seems like you need to speak a different language. If you\u2019ve spent any time in an online shooting forum, you know exactly what I\u2019m talking about. The world of firearms has its own jargon.\u00a0<\/span><\/p>\n

However, not everyone properly uses the lingo. (After all, how many times have we heard a magazine called a clip?<\/a>) For new shooters learning shooting fundamentals, the language of seasoned shooters can be confusing and intimidating. And the fact that gun people can be wary of anyone who doesn\u2019t speak fluent firearm, doesn\u2019t do a lot to help newcomers sort things out.\u00a0<\/span><\/p>\n

To compound the situation, the language of firearms has evolved with few solid rules. In many cases, the vocabulary seems to have a mind of its own, wandering in circles without an obvious pattern. This is particularly true when it comes to caliber. Throw in all the numbers, decimal points, and metric measurements and it’s enough to make a newbie\u2019s head spin.\u00a0<\/span><\/p>\n

In the interest of education, we are going to explore the basics of cartridge caliber designations. While this article targets the fledgling shooter, there\u2019s a good chance those with a little more experience will pick up something in here as well.<\/span><\/p>\n

What is the Definition of \u201cCaliber?\u201d<\/span><\/h2>\n

\"9mm<\/p>\n

Caliber is the nominal bore diameter of a firearm. It is measured in inches or millimeters. The term also applies to the diameter of a bullet.<\/span><\/p>\n

For clarification, \u201cbullet\u201d\u00a0 refers to the projectile fired by a round of ammunition. Although many uninformed media pundits will use the term bullet to refer to firearm ammunition, the \u201cbullet\u201d is only part of the package. The entire thing is a cartridge<\/a>.<\/span><\/i><\/p>\n

Imperial Measurements<\/h4>\n

Caliber is expressed in either metric or Imperial measurements, depending on where the cartridge was developed (Usually inside the United States versus pretty much anywhere else in the world. As usual, the U.S. likes to do its own thing.)\u00a0<\/span><\/p>\n

For example, “.22 caliber” or “.45 caliber\u201d are Imperial measurement designations. .22 and .45 is the diameter measured in inches. (When pronouncing these terms, you drop the decimal point. A .22 caliber firearm would be called a \u201ctwenty-two caliber,\u201d or shortened to \u201ctwenty-two cal\u201d or just \u201ctwenty-two.”)<\/span><\/p>\n

\"\"
A 9 mm projectile measures 9 millimeters in diameter at its widest point.<\/figcaption><\/figure>\n

Metric Measurements<\/h4>\n

Metric measurements are also common. For example, a 9mm handgun has a bore diameter of approximately nine millimeters. There is no decimal point and we drop the term \u201ccaliber.\u201d <\/span><\/p>\n

In other words, don\u2019t wander into the local sporting goods store and ask for a 9mm caliber. That is technically incorrect. The strictest definition of caliber is diameter measurement in inches. However, gun people will still use caliber in a general sense to refer to diameter no matter the measurement used.\u00a0<\/span><\/p>\n

For example, you might ask the question, \u201cWhat caliber handgun do you prefer?\u201d<\/span><\/p>\n

To answer, \u201c9 millimeter\u201d (or \u201c9 mil\u201d or even just \u201c9\u201d) is an acceptable answer. Most gun people understand you are referring to general diameter when you talk about caliber, so the answer isn\u2019t limited to standard English measurements. No one expects you to refer to your Glock 17 as a .355. In fact, if you did, you would probably get more than a few weird looks.<\/span><\/p>\n

Caliber Isn\u2019t Exact Math<\/span><\/h3>\n

If you are math junkie, caliber designations might actually give you a headache, because the numbers are rarely exact measurements. For example, .38 Special and .357 Magnum are both 38 caliber<\/a>, but the diameter of the bullet is actually 357 thousandths of an inch.<\/span><\/p>\n

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