## Ghostcrawler on the mechanics behind Armor Penetration

There is a great thread over on the Damage Dealing Forums started by a Rogue about the mechanics of the Armor Penetration cap/observed effectiveness. Armor Pen is a statistic that will allow an attack to ignore a given amount of armor.

The thread and the contents inside it are notable in that it is, by my recollection, the first time a Blizzard employee has given out the complete rundown of an in-game formula. While there have been hints and comments about how certain statistics impact the game from patch notes and game designer posts in the past, there has never been a "step a, step b, step c" like algorithmic definition to all those stats contained within the black box of theorycrafting.

In giving out the computations behind Armor Penetration, Ghostcrawler makes note to point out that Blizzard is not, and will not, get in a habit of delivering theorycrafting to players. They like the idea that players have to test out game mechanics, and that while the starting and end results are known, what happens in the middle of combat isn't written in stone. In the case of the Armor Penetration rating, they released it due to quite a bit of (somewhat) inaccurate information out there.

The armor penetration formula, and an example, after the break.

Ghostcrawler delivers the formula for the Armor Pen cap in the following bit of pseudo code (I've cleaned it a bit for readability sake):

Let C be the Armor Penetration constant.

if ( level < 60 )

Thus where a level 80 mob is being attacked, C = 15232.5. For a level 83 mob C = 16635.

The cap for Armor Penetration is then: (Armor + C) / 3

A quick example, used originally by Ghostcrawler but extrapolated upon here:

Assume a level 80 death knight NPC (note: non player character) has 9729 armor. C for level 80 mobs is 15232.5. The Armor Penetration cap is (9729 + 15232.5) / 3 = 8320.5. At this point the game will choose the lowest of two values, either 8320.5 or 9729, to represent the most armor which can be ignored. We'll call this value X. So X = 8320.5.

A person is attacking with 30% Armor Penetration. The game will then compute the amount of armor to be ignored against the previous value X, which means the amount of armor ignored on our level 80 death knight NPC is 2496.15 (30% of 8320.5), which we'll call M. M is then subtracted from the death knight's actual armor, which means the attack goes through against 9729 – 2496.15 = 7232.85 armor present.

Now if this is all Greek for you, don't worry. I wanted to get the information out there today. Look for a detailed guide, complete with pictures and diagrams, later this week.

The thread and the contents inside it are notable in that it is, by my recollection, the first time a Blizzard employee has given out the complete rundown of an in-game formula. While there have been hints and comments about how certain statistics impact the game from patch notes and game designer posts in the past, there has never been a "step a, step b, step c" like algorithmic definition to all those stats contained within the black box of theorycrafting.

In giving out the computations behind Armor Penetration, Ghostcrawler makes note to point out that Blizzard is not, and will not, get in a habit of delivering theorycrafting to players. They like the idea that players have to test out game mechanics, and that while the starting and end results are known, what happens in the middle of combat isn't written in stone. In the case of the Armor Penetration rating, they released it due to quite a bit of (somewhat) inaccurate information out there.

The armor penetration formula, and an example, after the break.

Ghostcrawler delivers the formula for the Armor Pen cap in the following bit of pseudo code (I've cleaned it a bit for readability sake):

Let C be the Armor Penetration constant.

if ( level < 60 )

C = 400 + ( 85 * targetlevel )

else C = 400 + ( 85 * targetlevel ) + ( 4.5 * 85 * (targetlevel – 59))

Thus where a level 80 mob is being attacked, C = 15232.5. For a level 83 mob C = 16635.

The cap for Armor Penetration is then: (Armor + C) / 3

A quick example, used originally by Ghostcrawler but extrapolated upon here:

Assume a level 80 death knight NPC (note: non player character) has 9729 armor. C for level 80 mobs is 15232.5. The Armor Penetration cap is (9729 + 15232.5) / 3 = 8320.5. At this point the game will choose the lowest of two values, either 8320.5 or 9729, to represent the most armor which can be ignored. We'll call this value X. So X = 8320.5.

A person is attacking with 30% Armor Penetration. The game will then compute the amount of armor to be ignored against the previous value X, which means the amount of armor ignored on our level 80 death knight NPC is 2496.15 (30% of 8320.5), which we'll call M. M is then subtracted from the death knight's actual armor, which means the attack goes through against 9729 – 2496.15 = 7232.85 armor present.

Now if this is all Greek for you, don't worry. I wanted to get the information out there today. Look for a detailed guide, complete with pictures and diagrams, later this week.

Filed under: Odds and ends

## Reader Comments (Page 1 of 3)

## gow Apr 19th 2009 6:16PM

@_@

## outlier Apr 19th 2009 10:16PM

I agree with the confused guy but what I'm thinking is with the time you spend doing the math behind all this, you can do the following;

1) Join a progression guild.

2)Get into Ulduar.

3)Get gear with high item levels.

4)Google the following; Elitist Jerks+(Name of Class)+(Name of Spec)+(Patch Number(3.1 obviously atm) and get all you need to know.

Really, you just need a few people figuring out the statistics for you, the first one to figure it out and a few independent sources to verify. I'm not saying that this article implies everyone is a mathematically inclined elitist, just that this is a example where society is better off allowing for specialization to solve the problem while the overwhelming population benefits. Besides,if BC is any indication, here is what tier progression will look like;

T7; Many best in slots but not completely elitist optimized, intended to get you hungry for better.

T8; Better itemization but still lacking more than likely through the set bonuses.

T9;Itemized very well (not to mention really cool looking) for class/spec combination with set bonuses that will leave you foaming at the mouth upon reading them.

## hold up Apr 20th 2009 11:47AM

@outlier

Yes, your right. A small section of the population should do all the computations for the not so smart people. But instead of throwing stuff out there and theorycrafting we should start charging the lazy ones for our time spent doing difficult math problems with hours of analysis.

Thanks for the idea!

## Vant Apr 19th 2009 6:20PM

That snapshot of "A Beautiful Mind" was a nice touch. :)

## elstor Apr 19th 2009 6:52PM

Fred is real!

## shoryu Apr 19th 2009 6:24PM

so basically armor pen can increase your melee dmg by the % of the armor it ignores. lets just say that ur armor pen is 30% and the targets armor is 20000 so at 83 boss (16635+20000)/3 =12.2116 so 12.2116 * .70 = 8548.16 and 20000-8548.16=11451.84 so where around 20k armor reduces physical dmg by about 50% armor of around 11k would reduce physical by about 30-40% so basically a 10+% increase in physical damage done. so armor pen isnt so useless on raid bosses. an arms war with the 10% armor pen plus 5 sunders would have a baseline of 30% armor pen and whatever else you add to it.

## Heilig Apr 19th 2009 7:12PM

Except, as the formula shows, a mob with more than 8500 ish armor will have the amount of armor that can be reduced capped at that number.

So, while "30% armor reduction" would be nice, the more armor the mobs have, the worse this stat is, just like before. The only difference from BC is that now it sucks for clothies, too.

Thanks for clearing that up for us, Mr. Street. I will continue to completely ignore this stat in favor of everything else but spirit.

## SmokeTheBear Apr 20th 2009 12:42AM

In the example above where the boss has 20k armor, the formulas would actually be:

(20000 + 16635) / 3 = 12211.67

X = 12211.67

M = 12211.67 * .30 = 3663.501

20000 -3663.501 = 16336.499

So the effective armor would be 16336.499.

20k armor for a lvl 83 boss would be (assuming current formulas for armor-based damage reduction are accurate) 54.59% reduction.

16336.499 armor for a lvl 83 boss would be 49.55% reduction.

Thus 30% armor penetration would increase your damage vs raid bosses with 20k armor by roughly 5%.

## Shoryu Apr 20th 2009 1:31AM

thats simply pathetic. armor pen really is the least useful dps stat. ill just apply my 4 sunders and not worry about it. im still trying to work my dps out of the rut the TG nerf put it in

## SmokeTheBear Apr 22nd 2009 12:07AM

Well, that's also taking 20k armor for bosses into account. I haven't seen any clear-cut numbers about boss armor in Ulduar, though it seems like 20k would be on the high end for bosses in there, given known values for other Wrath bosses being around 12k.

## Cptcharisma Apr 19th 2009 6:27PM

lol, yes its greek to me, i only got 53 in grade 12 calculus

## Jessamine Apr 19th 2009 6:34PM

This... is algebra...

## Pyratus Apr 19th 2009 6:40PM

No! THIS. IS. WARCRAFT.

## Shoryu Apr 19th 2009 6:43PM

no, this is SPARTA!!!

## Ulftar Apr 19th 2009 6:44PM

omg, i got the exact same mark in calculus in high school. I think it was a pity-pass.

## AyaJulia Apr 20th 2009 2:08AM

53 is a passing grade these days?

Sheesh, I had to get 70 at least, and that was only about eight years ago.

## doublebigmac Apr 20th 2009 1:00PM

NO, THIS IS PATRICK!

I'm not Sparta!

## Zhiva Apr 20th 2009 4:26PM

>only got 53 in grade 12 calculus

Um, I assume that "grade 12 calculus" is that which is called "Basics of higher math" in my country, and 100 is the maximum mark?

## Eternauta Apr 19th 2009 6:35PM

So, in that formula, 400 is the constant for Armor Penetration, or Armor Penetration RATING?

I suppose it's the secound one, because 400 is not a percentage.

Damn I'm confused.

## shoryu Apr 19th 2009 6:40PM

400 is the baseline armor not armor pen

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