Consider the following situation: a level 20 elementalist with 15 air magic uses Lightning Strike against a warrior wearing Gladiator's Armor (and not wielding a shield). Lightning strike has 25% armor penetration and the warrior has 80 AL versus elemental damage, which results in an effective 60 AL (80 * (1 - 0.25)). Against an effective 80 AL, lightning strike would have dealt 35 damage, but armor penetration will increase the damage to 501. This is roughly a 43% increase.
There are two sources of armor penetration, base armor penetration and bonus armor penetration:
- Base armor penetration is a set armor penetration value which is usually listed in game with text such as "this attack has 20% armor penetration." Base armor penetration does not stack, and only the largest value is used for any single hit. Sources include:
- Bonus armor penetration is an additional armor penetration value which is usually listed in game with a preceding plus sign, such as "+20% armor penetration." Bonus AP does stack with base AP and other sources of bonus AP. Sources include:
1 see Damage for additional information on damage calculations.