What is Mitigation?
Mitigation is the amount of damage that is reduced by your armour. You can find out what your mitigation against physical damage is against something the same level as you by mousing over your armour total on the character sheet in game. If you have 54% mitigation, then you would take 46% of the damage from the attack when it lands. Using those numbers, if the attack would hit for 10,000 damage with no armour, you would take 4600 damage from it. There's a hard cap of 75% mitigation on armour, easily testable in game, Blizzard has outright told us in past, and as you see in the code below from the basic WOW interface it gets set to 75% if the calculation were to come out higher than that.
Note that a lot of people call dodge and parry mitigation. We've been encouraging people to distinguish avoidance and mitigation by their definitions for a long while:
Main Entry: mit·i·gate
1 : to cause to become less harsh or hostile
2 a : to make less severe or painful
Main Entry: avoid
(...irrelevant definitions...)
3 a : to keep away from b : to prevent the occurrence or effectiveness of c : to refrain from
While a dodge or parry (or being missed) technically means you mitigated 100% of the damage, it also leads to confusion when trying to talk about the various gear strategies. Dodge, parry and miss are properly called avoidance.
When you block, on the other hand, that is mitigation since you are only preventing some amount of damage, and the rest gets through. Blocking can give up to an extra 10% mitigation, depending on what you're fighting and what your block value is.
How much mitigation does my armour give, anyway?
Happily, this is a question that is easily answered without needing to reverse engineer anything. We simply look in the PaperDollFrame.lua file in the basic WOW interface. This is the piece of code that displays all your stats on the character frame. It explicitly gives the mitigation formula for armour:
local levelModifier = attackerLevel; if ( levelModifier > 59 ) then levelModifier = levelModifier + (4.5 * (levelModifier-59)); end local temp = 0.1*armor/(8.5*levelModifier + 40); temp = temp/(1+temp); if ( temp > 0.75 ) then return 75; end ...
From this we see one thing immediately - with The Burning Crusade, the formula for mitigation has been significantly changed for level 60 and higher attackers. We note that in all cases, the formula for mitigation as a function of armour takes this form:
A
M = -----
A + K
Where K is a value based on the attacker's level (not your level!). When considering mitigation for attackers under level 60, and attackers level 60 and over, all that changes is the value of K. Let's first visit the old-style mitigation formula, which still applies for all attackers under level 60.
Under 60
From the above code, we see that if level is under 60, we still get K = (85*L + 400). Substituting back into the mitigation formula:
A
M = ----------------
A + (85*L + 400)
60 and beyond
From the above code, we see that if level is 60 or higher, the value of K is modified based on how many levels above 59 the attacker is. With a bit of manipulation, we get: K = (467.5*L - 22167.5). Derivation of that is left to interested readers. Substituting back into the mitigation formula:
A
M = -----------------------
A + (467.5*L - 22167.5)
That's pretty ugly. Here's the formula solved for level 70 and 73 attackers, which will be the interesting cases anyway:
A
M70 = ------------
A + 10557.5
A
M73 = ----------
A + 11960
Mitigation at selected points
Armour Level 70 Level 73 5000 32.1% 29.5% 10000 48.6% 45.5% 15000 58.7% 55.6% 17000 61.7% 58.7% 20000 65.4% 62.6% 25000 70.3% 67.6%30000 74.0% 71.5%
Wait, what? So when do I hit the 75% cap?
As always, the 75% cap is hit at 3*K (again, the derivation of this is left to interested readers).
For a level 70 attacker, 75% mitigation is at 31672AC
For a level 73 attacker, 75% mitigation is at 35880AC
Don't forget to read here about diminishing returns.
Blocking
Blocking is also a form of mitigation. Every time you block, you reduce the incoming damage by your shield block value (SBV). Depending on what you're fighting and how much block value you have, it can be a pretty significant amount of mitigation. More on blocking here
Defensive Stance
The warrior 10% mitigation bonus for Defensive Stance is multiplied with your mitigation from armour, (and is not included in the mitigation given in the tooltip for armour). That is, damageTaken = totalDamage x (1-mitigation) x (0.90)
For example:
- If you have 50% mitigation from armour, you have an overall mitigation of 55.0% in defensive stanceWhat about Magic?
When fighitng something that does magic damage, armour doesn't provide any mitigation at all. That's when we start breaking out the resist gear. The basics of how resistance works are found here. The best you can do with resistance, as with armour, is to achieve an average 75% resist rate. You get this by having a resistance against the school of magic equal to the (5 x mob level). For level 70, that's 350. For 73 that's 365. Note that spells and special abilities cast by mobs cannot be critical hits, so defense isn't nearly as important as resistance for high magic damage tanking where the magic comes from spells and/or special abilities.
On the other hand, elemental mobs deal melee damage that is elemental, and they can critically hit you with those melee attacks. Having some defense is good here, but it's often very important to maintain the high resistance even at the cost of defense. In general, maxed out resistance will mitigate more damage than the crit reduction would provide while taking more damage overall because of lower resistance.