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. The chance to critical strike can be viewed in the character pane under melee stats and is affected by agility, critical strike rating, and talents. Some classes have talents that increase the amount of bonus damage for critical strikes or talents that increase their critical strike rating. Attacks made by mobs can not result in a blocked critical strike, but this can result on a player attack. It can also be viewed by opening the spell book and mousing over the "attack" ability. Notable about critical strikes is that any non-spell attack on a sitting target will always result with a critical hit.

Critical Strike Rating
Critical Strike Rating is a combat rating found on gear, enchants, and gems. It takes approximately 22.08 rating to increase your critical strike chance by 1% at level 70 and 45.91 at level 80. As of patch 3.0.2, Critical Strike Rating affects melee,ranged and spells.

Agility
The agility you need to acquire 1% critical hit chance depends on your class and level. Keep in mind everyone has a base crit of 5% from agility. Only agility on gear adds to the base of 5%. Ex. If a level 80 paladin has 161 agility (90 base agility and 71 from gear) the crit chance from agility will be 5% + 71/52.08 = 6.36%.

Effect of increased crit or hit chance
Both increased hit and crit chance have a kind of "diminishing returns" mechanic built in. A 1% increase of either stat will not increase the total damage output by 1%, but usually by a little less. Consider the following Attack table:


 * 1) 2% base miss
 * 2) 5% dodge
 * 3) 5% parry
 * 4) 5% block
 * 5) 25% crit

Damage = BaseDamage * ((1.00 - 0.02 - 0.05 - 0.05 - 0.05 - 0.25) + 2 * 0.25) = BaseDamage * 1.08

(With 0% crit we'd do 83% of BaseDamage)

Now the same calculation with 26% crit chance: Damage = BaseDamage * ((1.00 - 0.02 - 0.05 - 0.05 - 0.05 - 0.26) + 2 * 0.26) = BaseDamage * 1.09

We increased the total damage output by 1% of the base damage. Since the total output is more than 100% of that base damage, the actual increase in total damage output is "only" 0.93%. If the total output is significantly greater than the base damage, this percentage will be smaller, if the total output is below the base damage, the resulting increase will even be higher than 1%.

What's better, +hit or +crit?
In principle they are equal. Which is better depends on circumstances. An increase in hit rate will usually yield a constant level of damage, whereas a high crit chance gives a spiky, more random damage distribution over time. An important factor is whether there are procs related to either hits or critical hits. Also, both ratings have caps (which are not fixed to a certain % but rather depend on multiple factors such as hit chance, enemy's level and defense rating). To hit can only be used to counter the base chance to miss (5% for one or two-hand users without any off-hand weapon, and 24% for dualwielders), whereas the crit chance cannot become higher than available space for hit chance. If a dual wielder attacks a target with a high chance to dodge or parry the attacker can lose crit chance because the attack table is full. (See the "Crit Cap" section below.)

For example, a dual wield in a raid, attacking from behind, with a 0 chance to hit, you have a maximum critical chance of 40%. Any additional critical chance increase is wasted. This number might seem high but take into consideration talents, potions, buffs, procs and skills that increase your crit rate to 50% or more, these are wasted.

From a raiding perspective, your miss chance increases by 3% (so 8% and 27% - base of 8% for special attacks) and increasing your Hit to at the very least cover your Special attacks is seen as more beneficial than increasing your Critical chance. After you have hit that level, you can focus more heavily on Critical Chance.


 * For single wielder classes, increasing your hit chance past 8% is ineffective.
 * For dual wielder classes (rogues for example), increasing hit past 8% is still beneficial, just not quite as much as that first 8% was.
 * For casting classes, hit rating is nearly always more valuable than critical strike rating, because of the two-roll spell attack system.

Crit Cap
White-damage attacks made by a player with fully-trained weapon skill against a mob 3 levels higher have a fixed 24% chance of being glancing blows.

Therefore, with no +expertise/+hit gear on, and no talents or racial abilities that increase Expertise or the chance to hit, attacks made by a level 80 dual wielder against a level 83 mob have the following table from the front:

Attacks against mobs made from the back cannot be blocked or parried (thus, attacking from behind will never trigger "parry haste" on the mob). Losing those values from the chart makes the "combined hit + crit" entry appropriately larger. Players cannot dodge, parry, or block attacks from the back.

It is not as bad if the same character attacks the same mob from the front with a two-handed weapon:

This is a 40% + your +hit + 2x your Expertise bonus crit cap.

Finally, consider attacking the mob from the rear, where the mob cannot block or parry:

All these crit caps could have been increased by increasing your Expertise (0.5% increase per point from the front, 0.25% increase per point from the rear) and by +hit (1% increase per percantage increase in your Hit chance).

Dual wield full raid buffs example from the front:

+0 hit +50% crit: 6.5% dodge, 14% parry, 28.0% miss, 6.5% block, 25% glancing blow, 20% crit = 30% of your crit rate did nothing +6% hit +40% crit: 6.5% dodge, 14% parry, 6.5% block, 22.0% miss, 25% glancing blow, 26% crit = 14% of your crit rate did nothing +15% hit +31% crit: 6.5% dodge, 14% parry, 6.5% block, 13% miss, 25% glancing blow, 31% crit, 4% hit = no +crit was wasted in this example

Dual wield full raid buffs example from the back: +0 hit +50% crit: 6.5% dodge, 28.0% miss, 25% glancing blow, 40.5% crit = 9.5% of your crit rate did nothing +6% hit +40% crit: 6.5% dodge, 22.0% miss, 25% glancing blow, 40% crit, 6.5% hit = no +crit was wasted in this example +15% hit +33% crit: 6.5% dodge, 13% miss, 25% glancing blow, 33.0% crit, 22.5% hit = no +crit was wasted in this example

DPS Implications
Hit Rating is very important due to the crit cap. The following shows the difference in white damage between various stat options:

Assuming 30% crit and +0% hit from the front, its 6.5% block for 70% damage 20% crit for 200% damage (impale doesn't work on white-damage attacks!) 25% glancing blow for 70% damage 48.5% miss, dodge, or parry for no damage per swing its an average of .065 * .7 + .20 * 2 + .25 * .7 = 62.05% of your damage per swing

Assuming you add +5% hit, the numbers become... 6.5% block for 70% damage 25% crit for 200% damage 25% glancing blow for 70% damage 43.5% miss, dodge, or parry no damage so per swing its an average of .065 * .7 + .25 *2 + .25 * .7 = 72.05% of your damage per swing

Enhancers
Various items can be added to your equipment (or imbibed) to increase your chance to critically hit.

Enchantments
- Shoulders
 * Greater Inscription of the Axe
 * Greater Inscription of the Blade
 * Inscription of the Blade
 * Greater Inscription of Vengeance
 * Lesser Inscription of the Axe
 * Might of the Scourge ...no longer drops

- Legs
 * Icescale Leg Armor
 * Nerubian Leg Reinforcements  Leatherworking only 
 * Nerubian Leg Armor
 * Nethercobra Leg Armor
 * Cobrahide Leg Armor

- Ranged
 * Heartseeker Scope
 * Stabilized Eternium Scope

Enchanting

 * Enchant Weapon - Accuracy
 * Enchant Gloves - Blasting
 * Enchant Boots - Icewalker
 * Enchant Boots - Surefooted

Racial abilities
Some races have racial abilities which increase the critical strike chance with certain weapons by 1%:
 * Dwarf: Gun Specialization
 * Troll: Bow and Thrown Specialization
 * Orc: Axe Specialization (as of patch 2.3.4, orc axe racial no longer gives 1% crit. It now increases weapon expertise by 5 for Axes and Two-Handed Axes.)


 * Prior to Patch 2.3.0, these racial abilities affected weapon skill instead.

Professions

 * Master of Anatomy from the Skinning profession