Your weight divided by your child's weight. This is how many times your child's size you are.
Example: 130 lbs / 25 lbs = 5.2 times the size of your child.
Keep that number in mind every time to hit your little kid.
I'm not trying to bash anyone, I'm just asking you to think about it. How frightened would you be as an adult if someone 3 to 6 times your size were coming at you to hit you? Even if it was just with an open hand (and of course not during whoopie time) wouldn't you be scared? Wouldn't you feel traumatized if someone that much bigger than you was "spanking" you to "teach" you to behave the way they expect and there was nothing you could do to defend yourself, no way for you to leave the situation?