Calibers and other forms of sizing.

[Jimmy Dean]

ok now, I would imagine that a 9 mil is 9 millimeters across?

but calibers, I looked up in the dictionary here on THR, but it did not give any units, just said that caliber is a measure of the diameter.

I am guessing that the calibers, such as 22, 45, 40 are all in hundreths of an inch? i.e. a 45 is 45 hundreths of an inch, or .45 inches, a 50 cal is 1/2 inch in diameter?

 

[Geronimo45]

Yes, 22, 40, and 45 are all hundreths of an inch, and are more properly .22, .40, .45.
The numbers for caliber run from (close) estimates to outright lies, though. .38 Special is .355, .44 Magnum is either closer to .41 or .42, for example.

 

[mpmarty]

.22 can be .223 or .224 diameter
.25 is .257
.270 is .277
.280 is 284
.30 is .308
.35 is .355 to .358
.40 is .40 how bout that?
.41 is .41
.44 is .429
.45 is .451 to .454
.50 as in Action Express is .500
.50 as in .50 BMG is .510

We will not cover metrics at this time.