Crushing Blow

Crushing Blow does damage that is a fraction of the current life of the victim. That fraction varies depending on monster type and whether it is a missile attack. That fraction is given by the following table :

Melee Missile

Normal monster 1/4 1/8

Others 1/10 1/20

This page computes an estimation of the mean number of hits to kill a monster.
For the calculation, I will use maxHP as the monster's life.

From the calculation, it should not be hard to see that crushing blow is most effective in an 8 player game, and crushing blow can be more effective than doubling the damage of your weapon (especially when your linear damage is low).

Basically, this calculator solves the difference equation:

A(x) = A(x-v)*(1-c) + A((x-v)*fraction)*c

with terminating condition

A(x) = 0 (for x < 1)

where v is the average damage, c is the chance of crushing blow, and x is the monster's life.

Note that this computation is performed on your machine.
How fast will it compute depends on the life of the target, and the speed of your CPU.
On my slow 233 MHz Pentium, a 100000 life target takes about 20 seconds.
So please be patient, especially if you have a slow computer.

T-Hawk suggested the initial crushing blow calculator back in Classic Diablo II.