Might try this Bullet Kinetic Energy Calculator:
Keep in mind that "Knockdown power" is not a real measure of bullet ballistics or force, it's mostly a Hollywood special effect. People that get hit just don't get knocked over or go flying through the air (and always into windows or some other glass..why is that?). It just doesn't happen and old Mr. Newton cringes everytime that scene is played!
Once you've selected thethe largest caliber handgunyou're comfortable with, select an ammo that suits your needs. If you live in an apartment with thin walls, JHP would likely be a better choice. If you have feed issues with JHP, EFMJ may be an option.All that's left then is practice, practice, practice. One critical shot from a .22 is worth more than any missed .45!
Accurate shot placement is first priority, max transfer of energy to your intended target is a close second. All else is really just personal preference based on cost and what your gun "likes".
The force required fora bullet to knock an attacker off his feet would also knock the shooter off their feet -Physics is Physics. This FBI report quotes a study that says being shot is similarto beinghit with afastball. I read that a 130 mph fastball is approx the same energy as an 1875 fps believe a 65mph fastball is approx equal to a 900fps bullet so a 90MPH fastball would actually have more energy and a greater transferrence of energy on impact. But being hit with a baseball doesn't stop attackers, critical hits to the CNS and vital organs orbleedout are what actually stop an attack(er).
In self defense, we only shoot to stop the attack, not to kill the attacker. Sometimes the latter is necessary and inevitible, but it's not the goal.
There are MANY references to this in books and on the internet. Here's probably the definitive reference (also attached):
Here's some other interesting reading:
The only guarantee for a one-shot knockdown is a critical CNS shot placement.
Hope this helped and Happy Reading!