Spell critical strike

Spell critical strike (often abbreviated as "spell crit") is when a spell or magical effect (most damaging spells, healing spells, some damage over time effects) has an increased effect. To see your chance to critically strike with spells, open your character pane and view your spell stats. Mobs are unable to get critical strikes with spells.

Spell critical strike chance is gained from both critical strike rating and intellect, as well as various talents and abilities.

Spell crit damage
The size of spell crits depends on the character's class and spec, as well as the spell cast:
 * All healing crits heal for 200% of the normal amount
 * All druid, mage, priest, shaman and warlock crits deal 200% normal damage
 * Elemental shaman crits deal 250% normal damage through Elemental Fury.

With damage over time, heal over time and area of effect spells, spell critical strike chance applies independently to each tick and each target.

Certain metagems, such as the Chaotic Shadowspirit Diamond, increase spell critical strike damage beyond 200%.

Base spell crit chance
The base chance to critically strike with spells is based on the Intellect attribute and a class specific constant.

Increasing spell crit chance
Spell critical strikes have a generally low chance of occurring, however, you can increase your crit chance in certain ways:


 * Attributes
 * Talents (some classes)
 * Equipment
 * Gems
 * Enchantments
 * Glyphs
 * Potions (temporary)
 * Buffs (temporary)
 * Debuffs (temporary)

Critical strike rating
The easiest method to increase the chance of a critical strike is to equip gear with the attribute "Increases your critical strike rating by 'x'." For some classes, critical strike rating is of less value. Unlike Intellect, critical strike rating increases the chance to get a critical strike equally for all classes.

Formula
For a level 85 character: crit chance % = (intellect / 648.91) + class constant + (crit rating / 179.28)

Note:
 * Talents that affect the crit chance of "all spells" (e.g.: Piercing Ice), or talents that specifically affect spells of a certain school, directly add to the calculated "Crit Chance %" on the character pane.
 * Talents that only affect the spell crit chance of a specific spell are NOT included in the spell "Crit Chance %" on the character pane.
 * Mousing over the "Intellect" value in your character pane will show you the Intellect portion of your spell "Crit Chance" (eg: "Increases Spell Critical Hit by x.xx%"). This works out to the "(INT/648.91)+ClassConstant" portion of the formula.

Using spell crit effectively
When evaluating the tradeoff between critical strike rating and other secondary stats, there are some things to consider:
 * Some classes have abilities or talents which proc off of spell critical strikes, as do some items.
 * Spell crit can lead to more unpredictable damage. As such, it can be powerful, but unreliable.
 * In group PvE, a string of "lucky" spell crits can pull aggro off the tank, possibly resulting in a dead caster.
 * In PvP, a string of "lucky" spell crits can take your opponents by surprise or simply overwhelm their defences, winning you the fight. Steady, predictable damage is easily anticipated and defended against; sudden spikes of damage are hard to anticipate and often impossible to defend against.

Spell hit or spell crit?
Without considering factors such as talents, a 1% increase in spell crit chance will result in a gain of 0.5% or 1% of a spell's base damage (depending on class/spec, see above), whereas a 1% increase in spell hit chance will always give a 1% increase of a spell's base damage. When dealing with 150% crits, this may make reaching the hit cap for your chosen area of play more valuable than increasing crit chance.

Numerous talents proc from crits (Ignite, Divine Aegis, Master of Elements), while many more proc from certain spell hits regardless of crits. These talents can significantly increase the desirability of increasing your crit chance. It should also be remembered that hit affects other types of spell such as ccs (Polymorph, Hammer of Justice, Psychic Scream), which can often be even more critical than damage.

In general, increasing crit chance without reaching your hit cap will lead to more unpredictable effectiveness, in terms of damage, talent procs and even ccs. This can be handy for PvP, where sudden burst damage can surprise and overwhelm opponents, but can also cause crucial spells to miss at critical moments.

There is still debate whether spell casting is based on a one-roll system (like "normal" melee) or not, although there is currently overwhelming evidence that it is a "two-roll" system - hit rolled for first, followed by a roll for crit.