Armor penetration

Armor penetration (often abbreviated as AP) is the amount of armor that an attack or spell ignores when calculating damage.

For example, an Air Magic spell that grants 25% armor penetration treats a foe with an armor rating of 80 as if it had only 60 armor, i.e. 80 - 25%*80. This would cause approximately ~41% more damage to the target than otherwise, since the increase in damage is dependent on the base armor rating.

There are two different types of armor penetration: base armor penetration and bonus armor penetration.

Base armor penetration

Base armor penetration is the non-stackable, fixed amount of penetration listed in a skill's description, e.g. "this attack has 20% armor penetration". If there is more than one source, only the highest value is used.

Source	Penetration	Requirements/Notes
Strength	1% per rank	When using attack skills
Air Magic spells	25%	Each one that deals lightning damage
Penetrating Blow Penetrating Chop	20%
Penetrating Attack Sundering Attack	10%
Cruel Was Daoshen	10%	Affects only Ritualist skills and only while ashes are held
Destructive Was Glaive	20%	Affects only Ritualist skills and only while ashes are held
Destructive Was Glaive (PvP)	10%	Affects only Ritualist skills and only while ashes are held
Sundering Weapon	10%
Spear of Lightning	25%

Bonus armor penetration

Bonus armor penetration is an additional amount of armor penetration, such as "armor penetration +20%". These do stack (adding them together) and add to the largest base armor penetration.

• Sundering weapon upgrades have a 10-20% chance to give attacks an additional 20% AP.
• Hornbows have an additional 10% AP on their attacks.
• Judge's Insight gives an additional 20% to attacks.
• The blessing Warrior's Might grants an additional 10% AP to attacks.

Notes

Anomaly.Armor Penetration does not simply subtract the listed percentage of armor, sometimes it subtracts slightly more. The exact mechanics are unknown.