Armor Penetration (WoW)

Armor Penetration, referred to as ArP, or ArPen, is an attribute that has become increasingly available with the latest season of PvP gear (season 3), as well as Tier 6+ equivalent gear. ArP effectively reduces the amount of armor your target has, and subsequently increases your physical damage done. ArPen's effectiveness depends greatly on the Armor of your target since the damage reduction (DR):Armor curve is exponential. Talents like the Rogue's Serrated Blades also increase ArP.

Damage Reduction (DR) Formulas

For the next examples, we will look at a target with 10,000 Armor, 5000 Armor and 2500 Armor, level 70 and use an ArP of 1000.

• 10,000/(10,000-22167.35+467.5*70) or 10,000/(10,000+10557.65) = 0.486 or 48.6% damage reduction before ArP.
• 5000/(5000+10557.65) = 0.321 or 32.1% damage reduction before ArP.
• 2500/(2500+10557.65) = 0.191 or 19.1% damage reduction before ArP.

After 1000 ArP you alter the formula like so:

• 9000/(9000+10557.65) = 0.460 or 46% damage reduction after ArP. A 2.6% difference.
• 4000/(4000+10557.65) = 0.275 or 27.5% damage reduction after ArP. A 4.6% difference.
• 1500/(1500+10557.65) = 0.124 or 12.4% damage reduction after ArP. A 6.7% difference.

As you can see, the damage gain from ArP increases dramatically the lower the Armor of the target becomes.

Effects On Damage Output

The changes in damage reduction can be deceiving, and you should not interpret a 2.6% change in damage reduction as a 2.6% increase in damage.

• 1000 physical damage against a target with 48.6% DR does 514 damage. Against 46% DR it does 540 damage, or a 5.1% increase in damage done.
• 1000 physical damage against a target with 32.1% DR does 679 damage. Against 27.5% DR it does 725 damage, or a 6.8% increase in damage done.
• 1000 physical damage against a target with 19.1% DR does 809 damage. Against 12.4% DR it does 876 damage, or an 8.3% increase in damage done.

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