The caliber is the size of the round your pistol fires. It is stamped on the barrel or slide, and you must use exactly that caliber. Here are the most common pistol rounds and what they are good for.
| Caliber | Bullet diameter | Recoil | Notes |
|---|---|---|---|
| .22 LR | .223 in | Very light | Rimfire. Cheap and quiet, best for training. |
| .380 ACP | .355 in | Light | Popular in pocket pistols. |
| 9mm Luger | .355 in | Moderate | The most popular pistol round. Affordable and effective. |
| .40 S&W | .400 in | Snappy | A former police favorite. Still common. |
| 10mm Auto | .400 in | Stiff | Powerful. Used for woods carry and hunting. |
| .45 ACP | .452 in | Firm push | A classic big-bore round, famous in the 1911. |
Which caliber should I choose?
- First pistol or one-gun owner: 9mm.
- Learning and plinking: .22 LR.
- Small pocket pistol: .380 ACP or 9mm.
- Big-bore fan or 1911 shooter: .45 ACP.
- Backcountry carry: 10mm.
Match your ammo exactly
- 9mm and .380 ACP use the same bullet diameter but are not interchangeable.
- .40 S&W and 10mm share a bullet diameter, but 10mm is longer and more powerful. Never mix them.
- Only shoot +P ammo if your pistol is rated for it.
- Check the barrel or slide and the owner’s manual before you buy ammo.
Learn more about rounds and bullets on Ammo Buyers Guide.com Pistol Ammo and Bullet Types.
Next step: see Pistol Brands, or head back to Where to Start.
Bullet diameters are nominal. Always use the ammo listed for your firearm.