ArP, Armor Penetration, & You - Understanding ArP

THIS IS WORTH THE READ...but it is a wall-o-text...and be forewarned there is some math involved...but don’t worry I did it all for you AND put a picture up to make it easier. :(

I’m still trying to research the Arms Pen thing. I read a few good articles but for the most part the advice has been: “Let your armor be your ArP and gem strength and crit”.

I know of a few people who have gemmed completely for ArP both fury and arms both PVE and PVP and quite honestly I to am as lost about a decent amount of ArP to have.

As it stands right now warrior ArP is a budding science and testing is being done on the pvp and pve front. ArP is something you definitely want to get, but how much is the question.

- Now if you’re running nax I wouldn’t worry about it to much as you don’t necessarily need it there.
- If you’re into Uldar then from what I can gather a good rule of thumb is to wait until your gear get’s you to 20-30% ArP then swap over some gems to reach 50% (which is 616 ArP)
- PVP is where things get a bit more...iffy. In a nutshell pvp is about sustainable burst damage (from an offensive standpoint at least) ArP can definitely lend to this, but again lots of testing remains.

Personally I’m still relying on crit, I believe I will be getting a Uldar mace this week and once that happens it’ll be difficult to not spec maces and stack ArP so hopefully we will see where this goes.

Below are the mechanics behind ArP which basically says that there are two numbers used in ArP calculations:
Number 1 – Target Armor
Number 2 – “the Cap”

The % in your tool tip is multiplied against the lower of these two numbers. Number 1 is easy to find, “the Cap” is a little more difficult and requires a small degree of math.

For a level 80 target, C=15232.5. For a level 83, C=16635.
“the Cap”= (Target Armor + C)/3

So basically of “the Cap” and the Target armor the lesser of the two values is selected then multiplied by the % in your tool tip to find just how much armor is reduced.

Take a deep breath
Because the math goes bonkers from here but I put a nice little picture to make it easier for my warrior brethren. (it's a crappy pic but the math is there if you look hard enough)What this picture does is basically identifies the point where your % tool tip effects either the Target Armor or the “the Cap”

At 7617 target armor we see that a level 80 is no longer having their ARMOR reduce, but rather “the Cap”. This is important because we can see that a 30% ArP affects things differently beyond this point (yellow line)

The green shows that the target armor is less than the “the Cap” so the 30% is used on the Green to calculate the armor ignored.

The Peach color shows that “the Cap” is less than the target armor so the 30% is used on the Peach to calculate the Armor Ignored.

Based on this we can see that a target with 1000 armor being hit with ArP of 30% does in fact have 300(30%) of their armor ignored.

We can also see that a target with 10k Armor has 2523(25%) of their armor ignored, which is less than the tool tip shows.

So to summarize the results the MORE armor something has past 7617 the LESS of a % your actually ArP reduces their armor by. In fact you can see the effectiveness of your ArP hits about 50% when a level 80 target has 30000 armor (druids)

So what does it all mean then...

You will get more bang for your buck attacking low armor targets and it would seam that classes sitting in the 7600 range of armor are the optimal of choice.

Vs plate and such ArP loses some of it’s effectiveness as far as ignored armor.

Once I find some decent numbers to shoot for I will post them here. Below is a link to another decent breakdown of ArP that I found very informative.
http://gurggalicious.blogspot.com/2009/06/armor-penetration-information.html

If you have any input on the ArP situation please feel free to leave a comment so we can all figure this out.

Originally posted by GhostCrawler:
We didn’t want Armor Penetration Rating to be too powerful against low armor targets, like it had been in BC. We also didn’t want Armor Penetration Rating to be too powerful against high armor targets.So, we decided on a system where there is a cap on how much armor the Armor Penetration Rating can be applied to. So, the first X armor on the target is reduced by the percentage listed in the Armor Penetration Rating tooltip, and all armor past that X is unaffected. Another way of understanding that is we multiply the percentage in the tooltip times the minimum of the two values: the cap, and the amount of armor on the target after all other modifiers.Computing the cap is a little tricky unless you are already familiar with how World of Warcraft armor works. There is an armor constant we’ll call C. C is derived as follows (in some pseudocode):If (level<60)c=400+85*targetlevelelsec=400+85*targetlevel+4.5*85*(targetlevel-59);for c="15232.5." c="16635.The" c="15232.5." 3="8320.5.">