Measuring Bullets in Caliber

You’ve heard it on your favorite cop show, “looks like the killer used a twenty-two,” or, “he was killed with a nine millimeter.” But, if you’re curious like I was, you’re asking yourself, “what the heck is a twenty-two and what does it mean anyway?”
Well, common sense would suggest that the numbers have something to do with size and that is exactly correct. When you hear various numbers being mentioned related to bullets, the number being referred to is what’s called the bullet’s “caliber”. Caliber is a unit of measurement related to a bullet’s size. Specifically, what’s being described is the bullet’s diameter.

To be even more specific, the caliber of a bullet is the measurement of the diameter of the slug (or projectile) part of the bullet cartridge. This is important because in some situations, the bullet casing can be wider than the slug itself. But the caliber is specifically describing the width of the slug portion. Caliber does not refer to the length or power of the bullet, but simply the diameter of the bullet.

The Bottom Line: The Width of a Bullet Determine’s Its Caliber

I know, you’re thinking, “but what’s a twenty-two compared to a nine millimeter?” Well, as with all measurements, there’s the American way and the Metric way of measuring. The metric is simple, a nine millimeter (9mm) is exactly 9mm in diameter. The American measurement is a little different. A twenty-two (or 0.22) is exactly twenty-two one hundredths (22/100′s) of an inch in diameter – or a little less than a quarter of an inch. Similarly, a 0.38 is 38/100′s of an inch, a .50 caliber is a half inch, and so on.