Waaaaaay back in hunters safety, in my pre-teen years, the instructor told us the guage/ caliber equivalence. I don't remember it. Does anyone know it.

If I'm not making sense, what I mean is, the diameter of a 12 guage bore is equivalent to what measurement in inches, i.e. caliber.

Same question for all guages.

Just curiosity here, no other point to this thread.

Thanks