The only common sense way to look at rounds carried, available, is based on what has happened in the past, history if you would. And what you can carry with your normal mode of dress, each one of us.
So, have you had, with in say a 50 mile radius, a home invasion, with multiple criminals? It could happen to you.
You need a Law Enforcement caliber, .38spl, 9mm, .40S&W, .45ACP. And a LE capacity. Why not?
At 78 YOA, I can dress anyway I want, and do. So I dress armed. Glock 19Gen4, 16 round capacity, spare 17 round magazine, Surefire flashlight, Benchmade folder.
I personally like accuracy, so the 147g Ranger T, by Winchester is my pick.
Non PlusP. Night sights are a must, TruGlo fiber optic, extended slide release, factory. Trigger, clean, crisp, 4lb.
The base plug to help in rapid reloads.
Shoot IDPA matches, good practice. Always carry.