For reference, 9mm is .354 inches.
.354 (9mm)
.357
.40
.45
.50
Plus, you can always get higher grain rounds if you want to add more stopping power for self-defense, but that's all just preference really.
A well-trained shooter can do some serious damage to a would-be attacker regardless of what caliber of pistol they're using.
I chose a 9mm handgun because the ammo is cheaper. So it doesn't hurt my wallet so bad when I go to the gun range
