!! Armor Penetration

Armor Penetration (ArP, ArPen, etc) is one of the more complex stats ever force-fed to us by Blizzard. In TBC, this stat was only really for PvP; in WotLK it became something you'd want to grovel at the feet of, if it had feet. It's often misunderstood and hard to boil down into something simple. Nonetheless, here I go trying to make it simple and understood.

First of all, if you're a caster and trying to understand how ArP works for you, shoo. ArP is for physical DPS first and foremost. Some tanks can make use of it for threat via increased damage, but it's definitely not a primary stat for them.

!!!! What is ArP?

It is the measure of how much of the target's armor you ignore. ArP has a hard cap of about 1400, which ignores 100% of the target's armor. That's the simple explanation; the real answer is extremely math-y. If you're a math-y type (I'm not), take a look [url:here|http://www.wowwiki.com/Armor_penetration#Technical_explanation_from_Ghostcrawler] and have yourself a wonderful time.

Where ArP gets confusing is that its value as a DPS stat is extremely variable. Its value doesn't rise on a linear basis; lightly armored targets will scoff at your 1337 ArP, while heavily armored targets will bear the brunt of your hurt feelings. In short, it's a weird stat.

!!!! What is "passive ArP"?

Passive ArP is the ArP you get from gear alone; no procs, no gems, no nothing.

!!!! What is the ArP "soft cap"?

The ArP soft cap is what you aim for when you have an ArP proc, such as the trinket Grim Toll. The soft cap plus the proc should equal 1400, the hard cap.

!!!! When do you want to stack ArP?

True to form, there is no simple answer for this. The basic idea for stacking it is to completely ignore it until you get to a certain range through passive ArP, then stack it like crazy until you reach another range, then ignore it again. When you begin to stack it is variable on your class and spec. When you cease to stack it depends on whether or not you have an ArP trinket, and which trinket you have.

If you've gone beyond the soft cap, you may be better off dropping the proc you're using and reaching the hard cap through gear and gems alone, or even just gear. This is quite possible with end-game leather in particular.

!!!! What value ranges should you look for?

As mentioned, the ranges vary depending on your class and spec.

Death Knights

Druids - ArP becomes more important than Agility when passive ArP (gear alone) is about 400-500. Agility regains its value when you've reached the hard or soft ArP cap. [url:Source|http://elitistjerks.com/f73/t63774-feral_dps_discussion/]

Hunters - "As a general rule, MM should start considering it at around 800-900 passive ArP (ArP from gear only, not counting procs or gems). BM with a ilvl 264 ranged weapon should start considering it at around 400 passive ArP. SV almost never wants to gem for ArP, except in the most extreme situations with insanely good gear." [url:Source|http://www.wow.com/2010/05/06/scattered-shots-hunter-gems/]

Paladins

Rogues

Shaman

Warriors

!! Armor Penetration

Armor Penetration (ArP, ArPen, etc) is one of the more complex stats ever force-fed to us by Blizzard. In TBC, this stat was only really for PvP; in WotLK it became something you'd want to grovel at the feet of, if it had feet. It's often misunderstood and hard to boil down into something simple. Nonetheless, here I go trying to make it simple and understood.

First of all, if you're a caster and trying to understand how ArP works for you, shoo. ArP is for physical DPS first and foremost. Some tanks can make use of it for threat via increased damage, but it's definitely not a primary stat for them.

!!!! What is ArP?

It is the measure of how much of the target's armor you ignore. ArP has a hard cap of about 1400, which ignores 100% of the target's armor. That's the simple explanation; the real answer is extremely math-y. If you're a math-y type (I'm not), take a look [url:here|http://www.wowwiki.com/Armor_penetration#Technical_explanation_from_Ghostcrawler] and have yourself a wonderful time.

Where ArP gets confusing is that its value as a DPS stat is extremely variable. Its value doesn't rise on a linear basis; lightly armored targets will scoff at your 1337 ArP, while heavily armored targets will bear the brunt of your hurt feelings. In short, it's a weird stat.

!!!! What is "passive ArP"?

Passive ArP is the ArP you get from gear alone; no procs, no gems, no nothing.

!!!! What is the ArP "soft cap"?

The ArP soft cap is what you aim for when you have an ArP proc, such as the trinket Grim Toll. The soft cap plus the proc should equal 1400, the hard cap.

!!!! When do you want to stack ArP?

True to form, there is no simple answer for this. The basic idea for stacking it is to completely ignore it until you get to a certain range through passive ArP, then stack it like crazy until you reach another range, then ignore it again. When you begin to stack it is variable on your class and spec. When you cease to stack it depends on whether or not you have an ArP trinket, and which trinket you have.

If you've gone beyond the soft cap, you may be better off dropping the proc you're using and reaching the hard cap through gear and gems alone, or even just gear. This is quite possible with end-game leather in particular.

!!!! What value ranges should you look for?

As mentioned, the ranges vary depending on your class and spec.

Death Knights

Druids - ArP becomes more important than Agility when passive ArP (gear alone) is about 400-500. Agility regains its value when you've reached the hard or soft ArP cap. [url:Source|http://elitistjerks.com/f73/t63774-feral_dps_discussion/]

Hunters - "As a general rule, MM should start considering it at around 800-900 passive ArP (ArP from gear only, not counting procs or gems). BM with a ilvl 264 ranged weapon should start considering it at around 400 passive ArP. SV almost never wants to gem for ArP, except in the most extreme situations with insanely good gear." [url:Source|http://www.wow.com/2010/05/06/scattered-shots-hunter-gems/]

Paladins - ArP is below any other stat found on plate for Paladin's, if at all possible it should be avoided. (About 60-70% of a retribution paladins damage is holy damage)

Rogues

Shaman

Warriors