TBC Armor Penetration Cap Calculator
Find the armor penetration rating that fully strips a target's armor — the ArP cap — and see the physical damage your current armor penetration buys.
Your armor penetration
You ignore 1776 of 3700 armor, leaving 15.4% damage reduction. Reach 625 rating to strip it fully (+35.0% physical damage vs zero ArP).
Advanced: formula & source
armorIgnored = ArP rating × 5.92; remainingDR% = remainingArmor / (remainingArmor + 10557.5)
In TBC, armor penetration rating ignores a FLAT amount of the target's armor (the percentage-based system came in WotLK). The cap is the target's effective armor after debuffs — so a fully-debuffed boss caps far lower than its sheet armor. Below the cap, ArP scales with increasing returns. Boss-armor reference values and the rating→armor conversion are web-sourced and pending an in-game pass (see manual-verification.md).
How TBC armor penetration works
Armor penetration rating ignores a flat amount of the
target's armor — about 5.92 armor per rating
at level 70. Damage reduction from the remaining armor follows Blizzard's
curve, DR% = armor / (armor + 10557.5) against a level-70
attacker. Because the armor debuffs strip most of a boss's armor first, the
practical cap is much lower than raw boss armor suggests.
Frequently asked questions
What is the armor penetration cap in TBC?
It's the armor penetration rating that ignores all of the target's remaining armor. Because TBC ArP ignores a flat amount of armor, the cap equals the target's effective (post-debuff) armor divided by the rating conversion — roughly 1300 rating for an undebuffed raid boss, and far less (~600) once Sunder/Expose Armor, Faerie Fire and Curse of Recklessness are up.
Does TBC armor penetration work as a percentage?
No — that's a common mix-up with WotLK. In TBC, armor penetration rating removes a flat amount of armor from the target, not a percentage. The percentage-based ArP system was introduced in Wrath of the Lich King.
Why is the practical cap so much lower than boss armor?
Because the armor debuffs do most of the work before your ArP even applies. Sunder/Expose Armor, Faerie Fire and Curse of Recklessness strip thousands of armor off a raid boss, so your armor penetration only needs to cover what's left — which is why ~1350 rating is the number people quote, not the figure raw boss armor would imply.
Is more armor penetration always better up to the cap?
Up to the cap, yes — and unusually, ArP gives increasing returns: each point ignored is worth more as the target's armor approaches zero. Past the cap it does nothing, so there's no reason to stack beyond fully stripping your target.