Effective Health Calculator
Note:
That while the above calculator will allow you to put in virtually any number you want, it is only accurate when using an Enemy Levels above level 60 because it is build using the following formula to calculate reduction percentage.
%Reduction = (Armor / (Armor - 22167.5 + 467.5 * Enemy_Level)) * 100
The above formula is for level 60 and up mobs. If you’d like to figure out your %Reduction for level 1-59 mobs you’ll have to use the following formula instead.
%Reduction = (Armor / (Armor + 400 + 85 * Enemy_Level)) * 100
For more information as well as the source of these formulas check out wowwiki’s page: Formulas:Damage reduction