Calibers: Inch / Millimeter Conversion
In the world of air-powered guns, caliber is often expressed in inches (the imperial notation, e.g. .177) or in millimeters (the metric notation, e.g. 4.5 mm). Both refer to the same thing: the diameter of the projectile. This conversion table lets you easily switch from one unit to the other and choose the ammunition suited to your gun.
| Caliber (inch) | Diameter (mm) |
|---|---|
| .177 | 4.5 |
| .22 | 5.5 |
| .25 | 6.35 |
| .30 | 7.62 |
| .357 | 9.0 |
| .45 | 11.43 |
| .50 | 12.7 |
How to read this table
The left-hand column shows the caliber in inches, as it is often engraved on guns or mentioned in technical specifications of imperial origin. The right-hand column gives the equivalent in millimeters, the most common unit in France and Europe. For example, a .22 caliber corresponds to a diameter of 5.5 mm, and a .50 caliber to 12.7 mm.
Knowing this correspondence is essential for ordering the right ammunition and accessories. A gun marked .177 uses 4.5 mm projectiles; a .50 caliber replica (such as some T4E launchers) fires 12.7 mm projectiles. Always check the exact caliber of your gun before ordering your projectiles or accessories.
Choosing the right caliber
The most common calibers for PCP and pellet rifles are 4.5 mm (.177), 5.5 mm (.22) and 6.35 mm (.25). Larger calibers, such as 7.62 mm (.30) or 9 mm (.357), equip more powerful models. The .50 caliber (12.7 mm) is found in particular on T4E-type defense and recreational launchers. If you have any doubt about the right caliber for your gun or your practice, our customer service is available to help.