Being serious for the moment. Mrs. Chillock says I need to. Damn!
This is a debate that the Mrs. and I have from time to time. She carries a small auto, at times she feels one mag is not enough. She now carries an extra sometimes two.
As for me, in MY experience (non- LEO) you should carry what you feel comfortable with.
I was taught, point shoot, once and follow through with a second. A typical "double tap". That is the way I shoot. Period. Bang, Bang. Next target. In the few times I have had to for self defense, never have I been asked why 2 shots? Why 4 shots etc. etc. I have never been asked why a BUG. Nor have I been accuse of "looking for a fight" by an attorney or anyone.
When I became of age and started to carry, I always carried one extra mag, no matter what the count of rounds. When I have had to defend myself, it had nothing to do with being in a "bad area I shouldn't have been".
Have I ever had to reload/change mags? Yes, once. Was it enough? NO. Thank goodness LE showed up as I ran empty. The off duty LEO, had a 38 special. He was out long before me. Normal situation? NO.
Several people quoted stats. Several people said one in a million. Hmmmm.... guess what? One in a million you'd have to reload. I did. One in a million you'd have to use that many rounds. I did. Both during the same situation. It happens... Odds are low, but it happens.
Under normal circumstances maybe 5 rounds is enough. I don't believe it. Plus I think this is subjective depending on to many variables such as where you live, where you work, where you have to travel to do everyday living, time of day/night, full moon/quarter moon, time of month/term of pregnancy, alignment of the stars..... Need I go on?
Obviously, you try to stay away from bad elements. But sometimes, all the weirdness comes together at the same time.
Carry what you are comfortable with, make, model, size, caliber of gun. Carry what you are comfortable with, 5 rnds, 10 rnds, 17 rnds, 2 backup mags, 4 backup mags and a trunk full of bulk ammo. Whatever, whenever. Just be legal and smart about it all.
And preferably have seal team six in standby, hovering above in a black helo. (Sorry Perfect One, back is sore today, can't carry my share of the seal team).