Let’s dive in to the meat and potatoes of today’s post. The effectiveness of Armor Penetration. You see this popping up on a lot of gear, such as Season 3 items and a lot of the loot coming out of Zul’Aman. The bottom line is that Armor Penetration is an awesome stat. Let’s look at why, and where the value should be placed.

The first thing we need to know is how Armor calculates damage reduction. The formula for calculating damage reduction is as follows:

For example, let’s take my current armor, which is 7181. Putting that into the formula, it looks like this:

Now if we look at myself on the Armory, this number coincides with what Blizzard’s tooltip is displaying, a damage reduction value of 40.48%.

Armor reduction is not a linear thing either. Take a look at this chart borrowed from WoWWiki to get a visual idea of what I mean:

There is a mathematical cap to the effectives of your Armor, usually a problem only high-end Druids have to concern themselves with. :)

OK, have we lost anyone? I hope not. Now we have a quick grasp of how Armor functions, we can start to talk about how Armor Penetration functions as well. Armor Penetration does exactly what it sounds like, it ignores your targets Armor, calculating the mob/person’s damage reduction against your attacks as if they had a lower Armor level due to this stat.

Let’s first take a look at the Armor value of many of the targets we would be dealing with.

So let’s run some hypothetical scenarios real quick so we can get an idea of how this would apply to us in-game. From the research done is this thread, which is reflected above, we know that Attuman the Huntsman has 7500 Armor. So if we plug that into our formula, the damage reduction we get is this:

That number also correlates correctly with the information provided by Elitist Jerks. With 41.53% damage reduction, we are capable of doing 58.47% of our possible damage. That is calculated by figuring out that if we attacked a target with zero Armor, our damage would be at 100%, and then subtract the target’s damage reduction. Given that, we can now see what our Armor Penetration will do for us. For instance, let’s say you have 500 Armor Penetration. We can now safely say that Attuman only has 7000 Armor. So let’s crunch that number:

So we now know that we are doing 60.131% of our total possible damage. This is a 2.84% damage increase for us when compared to 0 Armor Penetration. That was figured like this:

As you can see, we are just taking the percentage of the damage we can do after armor reduction with our Armor Penetration and dividing it by the pre-ArP damage. The actual number you will see is 1.028407~.

And not all Armor Penetration amounts are created equal either. Let’s do a comparison between 500 Armor Penetration and 1000 Armor Penetration. With full armor, Attuman has 41.534% damage reduction, allowing us to do 58.47% of our total possible damage.

With 1000 ArP, Attuman now has a damage reduction of 38.1%, allowing us to do 61.9% of our total damage. This comes as a 5.86% increase in damage when compared to attacking with no Armor Penetration. So if we subtract the damage increase from the first 500 ArP (2.84%) and subtract that from our new number (5.86%).

So we now see the second 500 Armor Penetration netted us a 3.02% damage increase, while the first 500 only gave us 2.84.

While that gain my seem very slight, remember that you are not the only person with Armor-reducing effects. Sunder Armor, Faerie Fire, Curse of Recklessness all are debuffs that are going to reduce the targets armor. So let’s say Attuman is now debuffed with these spells, including 5 stacks of Sunder Armor. With just those three abilities listed, Attuman is now down to 3490 Armor. This puts him at 24.8% damage reduction, already allowing us to achieve 75.2% of our total possible damage.

I found this calculator that calculates the DPS gain from Armor Penetration. The numbers it is producing seem accurate with all the math we have done thus far.

So hopefully no one’s head has exploded yet and that this is making sense. You can see why the Daggers of Bad Mojo are so highly rated on the Hunter’s desired weapon list, given that together you gain 240 Armor Penetration in conjunction with 162 Attack Power and 82 Agility (after enchanting them of course). :)

Another popular spreadsheet is this one, referencing damage reduction values against other players and their “class value.”

Well, that’s it for now. Hopefully I have all my research right. If you have any questions, comments, corrections, or concerns, leave them right here. Have a great weekend. Especially all of us who get a 3-day one. :D

Great Post. Armor Penetration for the win!

Hey on that note I’ve got a question for you on pet training then. Is it better to max out Natural Armor for more damage mitigation or go with Greater Stamina for more health?

What do you do?

Thanks.

I go with Stamina, as most of the things that cause my pet to die are unrelated to physical damage.

Glad you liked the post. :)

Wow, thanks for doing ‘my request’! And very informative, I’ve got a much better idea how it works now.

As for the calculator that did not produce the number you expected: it’s right. With 41.5% damage reduction, you’ll be doing 58.5% of your damage. When damage reduction goes down to 41.0%, that means that you’ll be doing 59% of damage. That means you’re doing 59/58.5=1.0085 of the damage you’d be doing without ArP, or a 0.85% increase in damage.

The interesting thing about ArP, as I gather it from your post, is that it scales with your gear. On Attumen, with 150 ArP, you will ALWAYS have a 0.85% increase in your damage. Meaning it will take your 500 DPS to 504 DPS, but your 1000 DPS to 1009 DPS.

But I’m not sure why it’s so great. With a full stack of Sunders, Faerie Fire and CoR, a hunter (and his pet does not) gains slightly over 1% damage increase from 150 ArP. 150 AP, on the other hand, would give a hunter a flat 10.7 DPS increase, and his pet would benefit with another 2 DPS. To gain a 12.5 DPS increase from ArP, the hunter, without counting his pet, would have to have 1200 DPS. That means that for a BM hunter, you’re pretty much looking at T6 gear.

I’m using rough numbers here, but it seems to me that stacking AP is a better idea than looking for ArP until you’re starting on T6 content.

Thanks for the clarification Basstian, I missed that in the Elitist Jerks thread. I updated the post and hopefully everything make more sense.

But you are right, stacking Armor Penetration is not easy to do. You find it higher iLevel gear, such as ZA, S3, BT, etc.

@Bastiaan

That 1200 dps figure is based on only having 150 armor penetration though, the more you have the greater the effect. In my normal gear, with 2 Daggers of Bad Mojo substituted for Breeching Comets with Delicate Crimson Spinels, I’m up to 651 armor ignore, and my guild is only in T5 content with the exception of a one-shotted Rage our first attempt (aside from a single wipe on trash due to an unlucky crush). I’d had Mojos in the bank collecting dust since I replaced them with Comets, but after this post I think I’m gonna pull them back out and give them a shot again :D

Jason,

yes, that’s a very good point of course. You’d be doing 4.9% more damage on Attumen because of your 651 ArP, and that’s again only increasing your damage, not your pet’s. So instead of 500 DPS, you’d be doing 525. The increase of DPS can also be achieved by getting +280 RAP. For 1000 DPS, the increase would be 50 DPS, or +560 RAP. And for 1200 DPS, the increase would be 60 DPS, equivalent to +675 AP.

Sounds to me like the turning point is 1200 DPS for 150 ArP and also for 650 ArP, making me believe that that turning point does not change with ArP.

Then again, Jason, that’s probably the DPS that you’re doing anyway.

I haven’t looked up the Elitist Jerk or any theorycrafting on this so I may be trying to reinvent the wheel here. But could someone confirm or disprove my belief that the point where ArP overtakes RAP in usefulness is 1200 DPS?

On a good night :) Most fights I spend a lot of time running around or trying not to pull aggro after threat dumps (LOOKING AT YOU LEO) to try for serious numbers… Imo there are too many fights in T5 content that we have to gimp our dps by running around. Tidewalker is just about perfect because we get to just stand and unload, and I’ve hit just under 1500 dps on that fight. Gonna give the extra armor ignore from Bad Mojos a try this week and see what happens. Hopefully I’ll have good news to report :)

The discussion makes me happy. :D I am glad people are taking something out of this.

It’s nice to have a forum to talk about things like this where there’s also a wealth of knowledge and insight available as well. I’ve gotten quite a bit out of your posts :) I also really like your progression posts and boss fight videos, I picked up Quartz today because I saw you had it, hoping it helps me weave shots a little better.

Also, grats on all the shiny new loots! I’m fairly jealous of all the pretties you keep getting…

Imagine if you could get a boss to 0 armor /drool.

I typed up some calculations last night, lemme know what ya think. (Sorry if it looks sloppy I was really sleepy)

head- coil of jungle stalker: 140 ArP

neck- choker of serrated blades: 175 ArP

ranged- amani longbow: 126 ArP

ring1- badge ring :126 ArP

belt- bladeangel belt: 77ArP

weapons- daggers of mojox2:280 ArP

cloak- dory embrace :112 ArP

hands: t6 gloves :140 ArP

feet: sunrage treads :126 ArP

pants- shifting camos: 175 ArP

ring 2: za ring: 126 ArP

bracers: steady bracers : 105 ArP

chest: shadowtooth cuirass: 210 ArP

shoulders- t6 shoulders: 126 ArP

total: 2037

5 sunders = 2600

ff = 610

imp expose x5 = 3075

executioner = 840

total = 9162 /drool

I’m not sure if this would be a huge boost up from your regular DPS, seeing as you are sacrificing stats like intellect(lots of leather) and hit rating for armor pen.

Lemme know what you think

Remember most bosses have 7700 Armor or so, so anything that could total more than your target boss’s armor can be replaced for more DPS stats. :)

But yeah . . . the armor pen makes a huge difference. It’s one reason Hunter’s like to see their DPS on Gorefiend. He has such low armor compared to bosses like Gurtogg.

I decided to give it a try.