Calibre facts for kids

A caliber (sometimes spelled calibre) is a way to measure the size of a gun barrel. It tells you how wide the inside of the barrel is. For example, a rifle with a barrel that's 0.22 inches wide is called a .22 caliber rifle. Guns are made to use bullets that are exactly the right size for their barrel.

How Caliber is Measured

Caliber is usually measured in inches or millimeters. In the United States, it's often given in inches, like ".22 caliber" or ".45 caliber." This means the barrel is 0.22 inches or 0.45 inches wide.

Sometimes, caliber is measured in millimeters. For example, a "9 mm" gun has a barrel that is 9 millimeters wide. Even though the original measurement might be in inches, it can be converted to millimeters, and vice versa.

There are many different sizes of calibers. Each type of gun is designed for a specific caliber of bullet. This makes sure the bullet fits perfectly and fires safely.

Images for kids

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  Rifle cartridges: from left: 50 BMG • 300 Win Mag • 308 Winchester, 7.62 × 39 mm • 5.56 × 45 mm NATO • 22 LR

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  A 45 ACP hollowpoint (Federal HST) with two 22 LR cartridges for comparison

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  Side view of a Sellier & Bellot 45-cal ACP cartridge with a metric ruler for scale

See also

In Spanish: Calibre (armas de fuego) para niños