My warrior dinged 80 last week. Now I am off gearing him to tank Naxx. As a healer or a DPS I cared very little about reduction to critical strikes. As a tank on the other hand this is a bread and butter stat. My raid leader spent a lot of times trying to explain to me why I need 540 defense. Despite of his heroic effort I only got half what I said.
After some extensively researching the topic I believe I have completely unraveled the mystery of defense. I am posting it here in hope it will help other newbie tanks. Although there are some good discussions on the web on the topic (such as tankspot), I found most of the guides didn't express clear enough the mathematical relationship between defense, critical strike and resilience.
What is my defense(Skill)?This is a simple and most elemental of all questions about defense. But believe or not most newbie tanks don't know how to figure out their own defense. I had trouble finding it myself the first time. What you need to do is look on your character sheet and select defense from the drop down menu. Your character's defense is shown on the second stat as illustrated above. Unless you are a tank this number is likely to be 400 at level 80 which means you have no extra defense gained from gear. The number you are shooting more is 540, which you gain by stacking +defense rating gears which is not the same as getting defense. Sounds confusing, I will explain below.
What is defense rating?Defense rating is the increase in defense you get from gear. When you get a piece of gear that says +70 to defense rating it doesn't mean you now magically gain +70 defense on the character sheet. These two numbers are related but doesn't have a 1:1 relationship. In order to understand the relationship we first need to understand critical strikes.
What is critical strike?Critical strike (often abbreviated as "crit") refers to 100% bonus
physical damage (twice your normal damage) that occurs as a result of an attack made with melee or ranged weapons. A Mob that is same level as you always have 5% chance to critical strike you. A raid boss is always considered 3 level above the character they hit.
And mob that is higher level than the character gets a bonus to the critical strike rating. For raiding any boss (or a mob which has a skull shown as level) can critically hit a tank at 5% + a bonus number. This bonus number is 0.6% for level 80 characters or 5.6% of total chance. Although 5.6% doesn't sound like a lot considering boss attacks all the time and tank gets hit all the time this stacks up pretty fast. So in order to prevent this from happening you will need a total of 5.6% reduction from critical strike when you equipping your character.
The magic 540If you have tanked you probably have heard this magic 540 defense before. How did this number come about? Remember on top we said each character has 400 innate defense at level 80? This means in order to reach the magic 540 you will need 140 defense extra from gears (again, note I said 140 defense, not 140 defense rating). We also know we need 5.6% reduction from critical strike at level 80. Therefore
5.6%/140 = 0.04%
or each point of defense you gain will reduce critical strike chance by 0.04%.
Now let's explain why there is a difference between defense rating and defense and their relationships. If you hover your mouse over a piece of equipment. It will tell you how much defense rating it has. Why doesn't blizzard just simply give you +Defense instead of +defense rating on a piece of gear? The answer is that a piece of gear would give you different amount of defense dependent upon your level. Since we are confining our discussions to level 80 only. Defense rating = defense x 4.92. How this weird multiplier came about again has to do with critical strike rating. We won't go into that at this is already complicated enough.
So simply put, if you want to gain 140 defense you will need +688 defense rating from all gear combined. Now you see that the task isn't as easy.
ResilienceBut wait. This gets better. There is another way to reduce critical strike against you. Yup. If you guess resilience you get full credit. Resilience is introduced in Burning Crusade as part of the new combat rating system. Although it is mostly used for PvP it has meaning for tanking. This is because:
1% Resilience will: - Reduce chance to be crit by 1%
- Reduce damage from all crits by 2.2%
- Reduce damage from DoTs by 1%
- Reduce mana drained by 2.2%
At level 80, 82.0 resilience rating equals 1% resilience or 1% reduction to critical strike against a character. Therefore,
1%/82 = 0.0122%
or every point of resilience will reduce critical strike chance by 0.0122%.
As we already discussed we want to reach a total of 5.6% reduction in critical strike chance. To gain amount purely from resilience you will need 459 total resilience.
Putting it togetherSo what have we learned here. You can reach the magical 5.6% critical strike reduction by stacking defense or resilience. Each point of defense you gain equals 0.04% reduction to critical strikes while each point of resilence you gain equals 0.0122% reduction of the same.
In addition, roughly every 5 points of defense rating gained from gear translate to 1 point in defense at level 80.
To look at this another way: each point of resilience gained from gear is worth roughly 1.5 times defense rating from game. A piece of PvP gear that offers +60 resilience will have the same effect of reducing critical strike as a piece of PvE gear that has +90 to defense rating (at level 80).
Assume your defense is X and your resilience is Y
0.04 * (X - 400) + 0.0122 * (Y) > 5.6%
Use a pratical example of my tank. He currently has 490 defense and 150 resilience. If you calculate using the equation supplied above.
He will have a total reduction to critical strike chance of:
0.04 * (490 - 400) + 0.0122 * 150 = 3.6% + 1.83% = 5.43%
This means he is still just below the cap with raid bosses who can critical strike him with 0.17% chance.
Now don't you wish you have paid more attention in your math class?
