Caliber to MM Conversion Chart for All Cartridges

Many shooters are confused because there are two different systems for measuring the bore diameter for a cartridge: (1) the caliber system measuring the diameter of the bore of the barrel in inches, and (2) the same measurement, but in millimeters. This page will explain the problem as clearly as possible.

The manufacturers of ammunition have done us no favors in making this easy to understand, but I’ve put together this handy resource so you can quickly see the equivalent naming conventions between mm and inches (caliber).

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Rifle Cartridge Caliber to Metric Conversion Table

Rifle Caliber NameCommon Metric NameBullet Diameter
.174.5mm.172″ (4.32mm)
.2045.2mm.204″ (5.2mm)
.2235.56mm.224″ (5.7mm)
.22 (lr)5.6mm.223″ (5.66mm)
.22 (not lr)5.6mm.224″ (5.7mm)
.2436mm.243″ (6.17mm)
.2576.53mm.257″ (6.53mm)
.2606.5mm.264″ (6.71mm)
.2706.8mm.277″ (7.04mm)
.2807mm.284″ (7.21mm)
.307.62mm.308″ (7.82mm)
.3258mm3.23″ (8.2mm)
.338.6mm.338″ (8.59mm)
.3669.3mm.366″ (9.3mm)
.3759.5mm.375″ (9.53mm)
.41610.6mm.416″ (10.57mm)
.5013mm.51″ (12.95mm)

If you’re like me, looking at the table above starts to make your head spin. There are some things in that table that just don’t seem right. That’s because the naming conventions for many of the most popular cartridges bend the rules of measuring in order to come up with a nice sounding name.

For example, the good old .308 Winchester is so named because the bullet is .308″ in diameter. Converted to metric, that’s 7.82mm, but most people would refer to it as a 7.62 because of its military distinction. The difference is that one measurement is the distance between the grooves (the cut out portions of the rifling in the barrel, and another measurement uses the measurement to the lands (the raised portion of the rifling). To make matters worse, the .308 is commonly referred to as a .30 caliber cartridge, which isn’t actually correct at all.

As you can see, the naming conventions of cartridges is complicated because ammo manufacturers like using clean, even numbers and to ignore the actual measurements.

Because the table above has to make some generalizations about particular cartridges, I’ve included the table below which lists each rifle cartridge separately so you can see the specific bullet diameter in inches and its exact metric conversion.

Common Handgun Calibers Converted to MM and Inches

Handgun CartridgeBullet Diameter in InchesBullet Diameter in MM
.22 LR.223″5.66mm
.357 Magnum.357″9.1mm
.380 ACP.355″9mm
.38 Special.357″9.1mm
9mm.355″9.02mm
.40 S&W.40″10mm
.44 Magnum.429″10.9mm
.45 ACP.452″11.5mm
.50 AE.5012.7mm

Fortunately, understanding the conversions between metric and imperial for handgun calibers is quite a bit easier because there are far fewer common pistol cartridges than there are rifle cartridges.

For the most part, handgun calibers are either 9, 10, 11, or 12mm.

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List of Rifle Cartridges and Their Bullet Diameters in Inches and MM

CartridgeCaliberBullet Diameter (mm)
.17 HMR0.1724.37
.17 Hornet0.1724.37
.17 WSM0.1724.37
.204 Ruger0.2045.18
.22lr0.2235.66
.22 Creedmoor0.2245.69
.22 Hornet0.2245.69
.22 Nosler0.2245.69
.22 WMR0.2245.69
.22-2500.2245.69
.220 Swift0.2245.69
.222 Remington0.2245.69
.223 / 5.560.2245.69
.224 Valkyrie0.2245.69
.240 Weatherby Magnum0.2436.17
.243 Winchester0.2436.17
6mm BR0.2436.17
6mm Creedmoor0.2436.17
6mm Remington0.2436.17
.25-06 Remington0.2576.53
.257 Weatherby Magnum0.2576.53
.26 Nosler0.2646.71
.260 Remington0.2646.71
.264 Winchester Magnum0.2646.71
6.5 Creedmoor0.2646.71
6.5 Grendel0.2646.71
6.5 PRC0.2646.71
6.5 Weatherby RPM0.2646.71
6.5 x 55 Swedish Mauser0.2646.71
6.5-284 Norma Match0.2646.71
6.5-300 Weatherby Magnum0.2646.71
.27 Nosler0.2777.04
.270 Weatherby Magnum0.2777.04
.270 Winchester0.2777.04
.270 WSM0.2777.04
6.8 Remington SPC0.2777.04
6.8 Western0.2777.04
.28 Nosler0.2847.21
.280 Ackley Improved0.2847.21
.280 Remington0.2847.21
7mm Mauser0.2847.21
7mm Rem Mag0.2847.21
7 SAUM0.2847.21
7 STW0.2847.21
7mm Weatherby Magnum0.2847.21
7 WSM0.2847.21
7mm-08 Remington0.2847.21
.30 Nosler0.3087.82
.30-06 Springfield0.3087.82
.30-30 Winchester0.3087.8232
.30-378 Weatherby Magnum0.3087.82
.300 Blackout0.3087.82
.300 PRC0.3087.82
.300 RUM0.3087.82
.300 Ruger (RCM)0.3087.82
.300 Weatherby Magnum0.3087.82
.300 Winchester Magnum0.3087.82
.300 WSM0.3087.82
.308 Winchester0.3087.82
7.62 x 39mm0.3087.82
.325 WSM0.3238.20
.33 Nosler0.3388.59
.338 Federal0.3388.59
.338 Lapua Magnum0.3388.59
.338 RUM0.3388.59
.338 Win Mag0.3388.59
.338-378 Weatherby Magnum0.3388.59
.340 Weatherby Magnum0.3388.59
.35 Whelen0.3589.09
9.3 x 62mm Mauser0.3669.30
.375 H&H Magnum0.3759.53
.375 Ruger0.3759.53
.378 Weatherby Magnum0.3759.53
.350 Legend0.3579.60
.416 Remington Magnum0.41610.57
.416 Rigby0.41610.57
.416 Ruger0.41610.57
.444 Marlin0.42910.90
.450 Bushmaster0.45211.48
.45-70 Govt0.45811.63
.458 Win Mag0.45811.63
.50 BMG0.51012.95
CartridgeCaliberBullet Diameter (mm)
6.5 PRC0.2646.71
Velocity (fps)Wind Drift (in)
2,9720
2,8070.2
2,6492.0
2,4954.3
2,3478.2
2,20413.2
2,06520.1
1,93227.6
1,80337.4
1,68048.8
1,56362.3
Muzzle Energy (ft-lbs)Drop at 500 Yards (in)
2,780-41
133-439
1,958-48
2,222-56
2,862-46
3,122-44
2,784-66
3,179-57
6.5 PRC6.5 Precision Rifle Cartridge
0.264Short Action
2.962018
CartridgeCaliberBullet Diameter (mm)
6.5 PRC0.2646.71
Velocity (fps)Wind Drift (in)
2,9720
2,8070.2
2,6492.0
2,4954.3
2,3478.2
2,20413.2
2,06520.1
1,93227.6
1,80337.4
1,68048.8
1,56362.3

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2 Comments

  1. If I reload 7.62×39 cartridge and the bullet diameter is listed the same as the .308 win at 7.81 mm why am I buying the advertised bullet diameter as .311 caliber?
    Just wondering? Have I missed buying the wrong bullets or is there a difference in the depth of lands and grooves in the rifling from the Russian/Chinese barrels? If so what difference is the American made barrel going to be? will it be a true .308 / 7.81? or does it matter since we are only talking about a mere maximum average pressure limits currently established at 45,000 psi.

    Hand loading does little to improve the velocity and killing power of the M43 round and most hunters using semi-automatic military style rifles do not reload simply because of the difficulty in recovering ejected brass. Nevertheless, there are a number of hunters using bolt action 7.62×39 rifles with hand loaded components.

    Fast burning powders such as IMR4198 and H4198 (ADI 2207) through to IMR 3031 and H4895 (ADI 2206H) give best results. Correct bullet diameter is 310” to .311”, with common bullet weights running between 123 and 125 grains. However it is possible to utilize 150 grain bullets (.311 /.312’) designed for the .303 British. Average velocities with hand loads are 2350 to 2400fps with 125gr bullets and 2000 to 2150fps with 150gr bullets, the former giving similar power to factory loads.

    The common question when reloading for Ruger rifles, is which bullet diameter to use. Ruger rifles have .308” bores, while typical 7.62×39 projectiles are of a wider diameter. The trouble is, if .308 projectiles are used, neck tension of re-sized cases is normally quite poor due to case necks being sized down to suit wider projectiles. In such instances, the hand loader may have no choice but to utilize .310” bullets. In practice, this is no different than the .303 Savage design premise (See .303 Savage text). Safe incremental load development is the key.

  2. scott russell says:

    do you have a chart comparing ” military calibers to millimeters.ie: 20 cal to 50mm ????– I live in Ogden Utah by Hill Air Force base. I am trying to get an idea of small calibers on a Gun ship (as an example) vs. large millimeter ammo.