Expertise

Expertise (also known as Exp and Ept) is an attribute introduced in Patch 2.3.0. One point of expertise decreases the chance that melee attacks made by the player will be dodged or parried by 0.25%.

Expertise rating
Note that there is a difference between "expertise" and "expertise rating". Expertise rating is typically gained from item bonuses, and for each 30.0272 expertise rating you equip, you gain 1 expertise at level 85. Expertise is typically gained from talents, and for each 1 point of expertise you reduce your chance to be dodged/parried by 0.25%. Thus it takes exactly 120.1088 expertise rating at level 85 to reduce your chance to be dodged/parried by 1%.

Racial bonuses
Certain players get passive expertise bonuses from their passive racial abilities:
 * Humans get +3 expertise with One or Two-Handed Swords and Maces.
 * Orcs get +3 expertise with One and Two-Handed Axes, and Fist Weapons.
 * Dwarves get +3 expertise with One and Two-Handed Maces.
 * Gnomes get +3 expertise with Daggers and One-Handed Swords.

Expertise caps
For boss-level mobs (which are calculated as level + 3) the soft cap is 6.5% dodge or 26 expertise (781 expertise rating), and the hard cap is 14% parry or 56 expertise (1682 expertise rating). Melee DPS classes will usually focus on the soft cap, since bosses cannot parry when attacked from behind. Some tanks will like to collect a lot of expertise in order to avoid boss parries, which may result in the Parry-Hasting effect. However, recently the boss Parry-Hasting effect has been disabled on some of the bosses.

For level 87 and below (heroic bosses and trash mobs in raids) the dodge and parry caps are the same.

Tanking
Expertise is of two-fold use to tanks. First, by reducing the target's avoidance, it improves a tank's threat generation (more of his/her attacks will land). More importantly, because mobs may attack more quickly after parrying an attack, expertise reduces the total damage that the tank may receive by reducing the chance that his target parries. The increase in attack speed varies (from 0-40% of the speed of the parried attack), and can stack if multiple attacks are parried in rapid succession, leading to a potential source of massive burst damage. However, this parry-hasting effect from when a boss parries has been disabled from most bosses except the last 3 in 25m TOC.


 * Note – The numbers here indicate the numbers necessary to stop your target from parrying and dodging your attacks, which apply primarily to tanks (due to tanks attacking the target from the front, and thus within the arc of parry-possible attacks). For dodge-only caps, please see DPS Expertise caps, below.
 * Also, please note that the Glyph of Seal of Truth is the only expertise-providing addition listed here that is not a talent or racial bonus. This provides ten expertise points (not rating) to the paladin while active, and requires that the paladin has Seal of Truth currently cast on themselves.
 * The expertise rating needed to achieve each expertise number is provided beside each number in parentheses. These numbers are rounded up, and the formula used is 1 expertise = 30.0272 expertise rating.

DPS
Melee DPS also benefit from expertise. With sufficient expertise, melee classes can attack their target from the front without being dodged or parried (although facing restrictions, such as those on Backstab or Shred, still apply). It is possible to have enough expertise to prevent dodges and parries, but parries are much harder to prevent, and players without such high expertise values should remain behind the target to prevent parried attacks from increasing the target's attack speed against the tank.

DPS will need a total of 6.5%, or 26 expertise, or 780 expertise rating, to avoid Dodges on yellow attacks against a raid boss.


 * Note that DPS expertise scores are assuming that the player is attacking the target from behind, and thus only take dodged attacks into account. For targets that can parry attacks (i.e. from with tanks, standing in front of the target), the expertise ratings required to make both parries and dodges impossible would be much higher (see Tanking Expertise Caps, above).
 * Also note that the Glyph of Seal of Truth is the only expertise-providing addition listed here that is not a talent or racial bonus. This provides ten expertise points (not rating) to the paladin while active, and requires that the paladin have Seal of Truth currently cast on themselves.
 * The expertise rating needed to achieve each expertise number is provided beside each number in parentheses. These numbers are rounded up, and the formula used is 1 expertise = 30.0272 expertise rating.

Expertise against bosses
The dodge and parry chances for boss-mobs is currently disputed, but combat parses tend to point at around 6.5% dodge and 14% parry. Assuming 6.5% dodge and 14% parry, a player would need 26 expertise (781 expertise rating) to negate a boss's dodge chance, and 56 expertise (1682 rating) to prevent parries.

To "cap" expertise against a raid boss, melee DPS need only concern themselves with the boss' dodge chance, provided that they attack from behind. This dictates a goal of 781 expertise rating. Tanks, however, attack from the front, and need to worry about both dodge and parry.

Expertise from talents
Death Knights gain 6 points of expertise from Veteran of the Third War, a talent specialization of the Blood tree.

Shamans can gain 4/8 points of expertise from Unleashed Rage, in the fifth tier of the Enhancement tree.