Warrior & Druid Guide to Tanking Mechanics

In this "guide" I will try my best to explain tanking mechanics I've learned during my 2+ years long career as a WoW Main Tank. I hope all new (and old) tanks will find this stuff both interesting and usefull and I truly hope it will help other tanks to "do their stuff" the best possible way.

The text is divided into several parts, detailing:
- Hitting, Missing, Dodging, Parrying and Blocking
- Bosses, Crushing Blows, Armor and Defensive Stance
- Comparing different types of characters
- Resistances and Stun Effects
- Aggro and Threat Mechanics 101

Disclaimer: This is not a "nerf" or "buff" text, although some of you will notice that it clearly states that druid and warrior tanks function differently and thus are good for different things. The text itself is NOT supposed to tell you "Who is better tank? Warr or Dr00d?". I deliberately omit Paladins, since I've never tanked with pally and thus am pretty ignorant on their mechanics.

Hitting, Missing, Dodging, Parrying and Blocking

WoW melee and ranged combat is resolved with "one-roll" principle which uses a single random number to resolve a single attack. Basic chance to miss for a mob is 5%, which means that a mob will hit you with 95% of its attacks. A mobs basic critical hit chance is also 5% so if you have no defenses the basic attack table looks like this:

90% Hit
5% Crit
5% Miss

Your Dodge, Parry and Block chances are deducted from the "Hit%" category, meaning that if you have 15% dodge the attack table looks like this:

75% Hit
5% Crit
15% Dodge
5% Miss

Now, both Defense score and Resilience have the effect of "reducing chance of critical hit", what this means is that the chance of Crit is replaced by a similar chance of hit. This is capped with 490 defence which reduces Crit chance of level 73 mobs and Bosses by 5,6% . To be Crit Immune against lvl 70 mobs requires just 475 Defence. Because of their wonderfull talent that reduces chance to be criticall hit by 3% feral druids have it a bit easier and need only 415 Defence to reach Crit Immunity.

Also in reality Boss miss rate is 5% PLUS the extra miss from defense of the tank (defense-350)*0.04
Miss, block, parry and dodge rates are lowered by 0.2% for each level the mob has over the tank. Thus against bosses all defense numbers are lowered by 0.6%. That's why you need not 5% but 5.6% crit avoidance to lower crit chance to 0. However, in following examples I'll simplify this by giving Druids an increased 2% miss rate (consistent with 415 defense) and Warriors an increased 5% miss rate (consistent with 490 defense). For simplicity I assume dodge and parry artes have already been calculated with the level difference in them.

Also do note that stacking defense is still valuable after reaching Crit immunity, since defence gives increased miss chance and also displays a little bonus to you existing dodge, parry and block chances. Stacking resilience after Crit immunity has been reached is, however, useless.

All of the above means that if you have 490+ defence and 15% dodge the attack table looks like this:

75% Hit
15% Dodge
10% Miss

This is the place where the benefits of avoidance start to show... Imagine a mob that hits for 1000 damage and crits for 2000 damage (unmitigated). Against a mage with 10% dodge attack table looks like this:

80% Hit (1000)
5% Crit (2000)
10% Dodge (0)
5% Miss (0)
Expected damage per attack (Edmg): 900

Compared to tank with 490 defence, 15% dodge and 15% parry, whose attack table looks like this:

60% Hit (1000)
15% Dodge (0)
15% Parry (0)
10% Miss (0)
Edmg: 600

The final thing here is the Block. Blocking works a bit differently. Block chance coverts "Hit" to "Blocked xxx damage" result. XXX here is the Shield Block Value, which is a sum of shields block value, item bonuses, str/20 and talent bonuses. Lets say that the tank in that example has a SBV of 500 and block rating of 30%. The attack table looks like this:

30% Hit (1000)
30% Block (500)
15% Dodge (0)
15% Parry (0)
10% Miss (0)
Edmg: 450