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).


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
.40 S&W.40″10mm
.44 Magnum.429″10.9mm
.45 ACP.452″11.5mm
.50 AE.50″12.7mm

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.


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

CartridgeCaliberBullet Frontal Area (in2)Avg Muzzle Energy (ft-lbs)
.17 Hornet0.1720.023622
.17 WSM0.1720.023398
.17 HMR0.1720.023240
.204 Ruger0.2040.0331,325
.220 Swift0.2240.0391,766
.224 Valkyrie0.2240.0391,519
.22 Nosler0.2240.0391,613
.22 Creedmoor0.2240.0391,769
.22 WMR0.2240.039276
.223 / 5.560.2240.0391,499
.22 Hornet0.2240.039680
.222 Remington0.2240.0391,165
.243 Winchester0.2430.0461,958
6mm BR0.2430.0461,712
.240 Weatherby Magnum0.2430.0462,099
6mm Remington0.2430.0461,953
6mm Creedmoor0.2430.0462,125
.25-06 Remington0.2570.0522,201
.257 Weatherby Magnum0.2570.0522,675
6.5 Creedmoor0.2640.0552,231
6.5 PRC0.2640.0552,780
.260 Remington0.2640.0552,273
6.5-300 Weatherby Mag0.2640.0553,395
.26 Nosler0.2640.0553,125
6.5-284 Norma Match0.2640.0552,462
6.5 x 55 Swedish Mauser0.2640.0551,983
.264 Winchester Magnum0.2640.0552,766
6.5 Weatherby RPM0.2640.0553,098
6.5 Grendel0.2640.0551,447
.270 Winchester0.2770.0602,862
.270 WSM0.2770.0603,072
.270 Weatherby Magnum0.2770.0603,176
6.8 Western0.2770.0603,011
6.8 Remington SPC0.2770.0601,624
.27 Nosler0.2770.0603,513
7mm-08 Remington0.2840.0632,528
7mm Rem Mag0.2840.0633,122
.28 Nosler0.2840.0633,678
.280 Ackley Improved0.2840.0632,912
.280 Remington0.2840.0632,873
7mm Weatherby Magnum0.2840.0633,482
7 SAUM0.2840.0633,004
7 STW0.2840.0633,458
7mm Mauser0.2840.0632,330
7 WSM0.2840.0633,255
.308 Winchester0.3080.0752,784
.300 Winchester Magnum0.3080.0753,827
.30-06 Springfield0.3080.0753,179
.300 WSM0.3080.0753,718
.300 Weatherby Magnum0.3080.0754,092
.300 PRC0.3080.0754,246
.300 RUM0.3080.0754,135
.30-30 Winchester0.3080.0751,942
.300 Blackout0.3080.075998
7.62 x 39mm0.3080.0751,608
.30 Nosler0.3080.0754,111
.300 Ruger (RCM)0.3080.0752,948
.30-378 Weatherby Mag0.3080.0754,666
.325 WSM0.3230.0823,596
.338 Win Mag0.3380.0904,164
.338 Lapua Magnum0.3380.0904,851
.338 Federal0.3380.0903,340
.340 Weatherby Magnum0.3380.0904,674
.33 Nosler0.3380.0904,799
.338-378 Weatherby Mag0.3380.0905,035
.338 RUM0.3380.0904,694
.350 Legend0.3570.1001,907
.35 Whelen0.3580.1013,932
9.3 x 62mm Mauser0.3660.1054,017
.375 H&H0.3750.1104,560
.375 Ruger0.3750.1104,780
.378 Weatherby Magnum0.3750.1106,004
.416 Ruger0.4160.1365,498
.416 Remington Magnum0.4160.1365,123
.416 Rigby0.4160.1365,166
.444 Marlin0.4290.1453,067
.450 Bushmaster0.4520.1602,810
.45-70 Govt0.4580.1653,138
.458 Win Mag0.4580.1655,063
.50 BMG0.510.20412,600

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  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 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.

  3. Patrick Lowe says:

    This a great list! makes more sense than a lot others. I have one question. What/where would 5.45×39 fit in each table you have listed?

    Would it be ok for me to print you conversion tables to use at my reloading bench?

    Thank you for your time

    1. Luis Mario Garcia says:

      Reloaders would find these
      measurements useful.

    2. If I recall correctly, the 5.45×39 is the same projectile as a 5.56 nato (.224 diameter)

  4. Joe Bendix says:

    Hello, the bottom of the bottom chart, – the “PRC” is just a reference, or the table collapsed, format? I’m confused, – but, too, realize that there does not horizontally line up with any above. If it’s an implied analogy, I sort of get it, but not clear, – if you don’t mind.

    I just considered my Dad’s 8mm x 51R Lebel, Berthier Carbine for (shooting) then, reloading. I realize I can, and will deconstruct the Privi Partizan rounds offered. However, having read for 8+ hours see the Bullet diameter per the drawings and if/not using Cast Bullets (to boot), is/is not .323. Rather… could be .324 – .327 or even per Cast Bullets, .310-.311 (max I’d say).

    The PPU Bullet in “todays”, as of this msg are, .323 – .324 digital caliper (you have to make sure your “touch” is “plumb” to the bullet, so to speak). Finding .327 FMJ or any kind, is a challenge. However, .324 Cast Bullets (teflon coated too) seem readily available as of “today” (since 8mm Mauser used, I read).

    I fully realize one just needs to just “shoot” and see, et alia and per YOUR weapon, etc. However, when one is trying to DILIGENTLY 🙂 do their first (for me), 1) minimal 2) start load knowing all the variables to then consider going forward, well, – “how I landed on this article”.

    So, there are many IMPLIED questions. As well, implied self reflection answers too. One does not find spec on (if even so prolific in use of the St. Atiene 8mm Lebel Carbine/Rifle), … spec on e.g. Barrel Lands and Grooves. Folks just load and shoot I guess? I pay close attention to Max Pressure. For that C.I.P. ~ 46Kpsi. I know “start” loads are not “minimun” loads per OEM-Powder “projections” (I can do math too 🙂 ). I am a near Subsonic bug for some reason, – “skill”?, anyone can top off a shell, OMG and see what happens. But, Subsonic and check, “effectiveness” (lethal aspect) for hunting is an art that does not make it out of hidden notebooks of more in the “sniper” world, prep.

    So, I hope my teflon, .324 cast bullets don’t keyhole from the muzzle and etc. I just thought, from your article above, – well, maybe I just rabbit trailed it in the moment, but wonder your thoughts on this particular, well followed but POORLY Load Data Offered round from since (modernly loads) 1916, making it to the 1980s in LEO use even I read, – in the EU.

    I look forward to your response, if even do? These internet blogs are somewhat ad hoc, but see you have a YT channel, so, we’ll see! 🙂

  5. Why was the British WWII .303 skipped in all lists? I may be rare in the USA (?) ,. but in many parts of the world the Lee-Enfield, Bren and other weapons in that caliber are stil in use and plentiful, too.

  6. Awesome info, those numbers really helps.