Project Lore

Honestly, I really didn't plan on covering Armor Penetration as part of this reoccurring column. For starters, the statistic is largely a junk statistic, due to its low usage on our fancy pieces of gear. Mainly, it's because the stat has never been fully understood, until now. A Blizzard Poster by the name of Ghostcrawler - you may have heard of him - revealed the in-depth calculations behind the statistic and ultimately what has had theorycrafters confused since its inception. To my knowledge, this is the first time Blizzard has revealed a formula, and only because of all the confusion surrounding it. Thanks to Patch 3.1 and some friendly pointers from Heartbourne, I've been on a bit of a math kick, which made yesterday's post all that more interesting to me. I must warn you that this discussion is going to have Algebra, serious algebra. Before we get into the complexity of the formula, here are the three things that seem to have held the theorycrafting up for so long. If you aren't a math fan hopefully the bullet points will help you grasp the concept. Otherwise, allow your eyes to glaze until the conclusion. Up To: This is a key phrase in the stats' tooltip that seems to be overlooked often. Simply put, the number displayed is the maximum percentage of armor that can be ignored. It isn't a guaranteed number because of the following two pieces that Ghostcrawler revealed. Constant: Blizzard didn't want Armor Penetration to be too powerful at the high or low end (read level) of the spectrum so they came up with this little diddy. The magic Armor Constant (will be refereed to as 'K' below) is an easy to calculate number that changes significantly when a mob is over level 60. Cap: The Cap, combined with the K, causes the "Up To" statement in the tooltip. If the Cap is lower than the target's armor, then said Cap is used in the Armor Penetration calculation rather than the actual target's armor. If this is the case, then the effective armor reduction will appear lower than the stat lists. The numbers for the first example are being lifted directly from Ghostcrawler's post on the topic, but to try and reduce confusion, I have left some extraneous information out and added additional explanation. If you grasp the original post, then the following block will be redundant. Our formula will focus solely on endgame content, level 80 and level 83 (boss mob) NPCs. Important numbers: Level 80 Constant (K) = 400+85*targetlevel+4.5*85*(targetlevel-59) = 15232.5 Level 83 Constant (K) = 400+85*targetlevel+4.5*85*(targetlevel-59) = 16635 Armor Cap = (targetarmor + K)/3 Example Mob: We will stick with Mr. Street's example, a level 80 warrior creature with 9729 armor. The player attacking has 30% Armor Penetration and no other modifiers. Calculation: Our armor constant (K) in this case = 15232.5 Armor Cap = (targetarmor + K)/3 = (9729 + 15232.5)/3 => 8320.5 The formula choses the lower amount (Armor Cap or actual armor) to apply the penetration stat (.30) to: ArmCap * ArmPen = lost armor => 8320.5 * .30 = 2496.15 Thus 2496.15 of the target's armor is ignored, effectively leaving the creature with 7232.85 armor: armor - armor lost = effective armor => 9729 - 2496.15 = 7232.85 Comparison: If it wasn't for the "Up To" statement then the calculation would certainly be off, since the player only sees a reduction of 25.66% of the target's armor. Due to the usage of the Armor Cap, the Armor Constant was selected, reducing the amount lost below the 30% that you may have expected. Example Boss: For our quicker second example we have selected a boss mob with 25000 armor being attacked by a toon with 30% Armor Penetration. Calculation: K = 16635 Armor Cap = (25000 + 16635)/3 => 13878 lost armor = 13878 * .3 = 4163.5 effective armor = 25000 - 4163.5 = 20836.5 Percent lost = 4163.5/25000 = 16.6% Conclusion: Armor Penetration is certainly not a statistic that you should be gearing out for. As you can see, your penetration percentage actually goes down against a well armored opponent. The original poster of the thread claimed that the toon in question had 116% Armor Penetration, but only reduced the target's armor by 66%. Talk about a loss. Although we may not have known the mechanics behind the calculation before, theorycrafters were correct in assuming that all our other stats are more important. Gear for Hit, Expertise, Agility, Attack Power, Strength, etc, as Armor Penetration is a third rate stat for Melee DPSers. For rogues, warriors, death knights and feral druids, the statistic should be weighed above Intellect and Spirit, but below seemingly every other modifier.

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