I have to agree with MLeake. I would say no less than 4-5 magazines per pistol, but most have no less than 12 magazines; I like more for my single stack handguns. It’s less need than efficiency when at the range and doing drills. I like to load up the night before, but more importantly, I can run through several drills without interruption. If your shooting drills (or competitive shooting) involve at least a few hundred rounds, it’s much easier with a dozen or more magazines. You need at least one for self defense, but if you’re serious about practicing several magazines will make your practice more efficient and consistent.