So I have been curious about where the number 10 came from, as far as anything over 10 is high capacity. I've also been curious about what the average capacity of a handgun is these days. My google fu has been failing me on this. Right now I am curious but I may invest the time in this to make it info an info graphic depending on what I find. I have a feeling the the average magazine size is really something more like 12-13 rounds, but I know 45s may skew this. I don't have the time to look up X number of guns in X calibers and figure out how many rounds are in a standard magazine. So I am hoping I can get people to provide me with some info and give me average magazine size for the guns they own. I'd like to break this into the 3 common calibers, 9mm, 40cal and 45cal. I own four 9mms witness P 15 rounds S&W 5906 15 rounds P-11 10 rounds Hi-power 13 rounds 9mm average is 13.25 rounds for what I own. Added: I'm interested in factory mag size here. What ever came with the gun, not what you have gotten after market. Also please break them out by caliber, and if your not comfortable saying what you have, or how many you own, don't. Just give me a caliber and average capacity for what you own.