| Intellect per crit % | |||
|---|---|---|---|
| Class | Expected @ 60 |
L. 60 1% Crit |
L. 70 1% Crit |
| Warlock | 200 | 60.6 | 81.92 |
| Druid | 192 | 60.0 | 80 |
| Shaman | 259 | 59.5 | 80 |
| Mage | 286 | 59.5 | 80 |
| Priest | 160 | 59.2 | 80 |
| Paladin | 106 | 54 | 80.05 |
Spell critical strike (often abbreviated as "spell crit") is when a spell attack does extra damage. A spell critical strike effect is when any other effect (usually, but not limited to, a 
[Heal]) has an increased effect.
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
- Potions (temporary)
- Buffs (temporary)
Spell critical strikes deal 150% normal damage without talents; however, most spellcasting classes have talents to increase it, most commonly to 200% normal damage. Spell critical heals will only heal for 150% of their normal amount.
The base chance to critically strike with spells is based on the Intellect attribute. To see your chance to critically strike with spells, open your character pane and view your spell stats; however, talents that only increase the critical strike chance of certain spells (such as 
[Incineration] and Force of Will) will not be included in the character pane.
Spell Critical Strike Rating
The easiest method to increase the chance of a critical strike is to equip gear with the attribute "Improves spell critical strike rating by 'x'." For some classes, spell critical strike rating is of less value.
Unlike Intellect, spell critical strike rating increases the chance to get a critical strike equally for all classes. At level 70, 22.1 spell critical strike rating increase the chance to critically hit with a spell by 1%.
Formula
For a level 70 character:
- Every class except Warlocks uses: (Intellect/80) + (Spell Critical Strike Rating/22.08) + Class Specific Constant
- Warlocks use : (Intellect/82) + (Spell Critical Strike Rating/22.08) + Class Specific Constant
- Class Specific Constants:
- Druid - 1.85
- Hunter - 3.6
- Mage - .91
- Paladin - 3.336
- Priest - 1.24
- Shaman - 2.2
- Warlock - 1.701
- Rogues and Warriors have a spell critical strike chance of 0% no matter what their Intellect is. However, the Warrior ability
[Thunder Clap] uses Spell Critical Strike Rating to determine the chance to crit.
Using spell crit effectively
When choosing between equipment with higher spell critical strike or higher +spell damage, 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 a group, a string of spell crits can lead to pulling aggro off the tank (and possibly a dead caster).
- Many spells, particularly DoTs, cannot crit. Spells that have a direct damage component and a DoT component (e.g. [Holy Fire]) are able to crit on the direct damage component but not the DoT.
- As a general rule, even though there are exceptions, increasing your pure spell damage is more effective damagewise than increasing your critical strike rating.
Spell hit or spell crit?
All other things being equal and without considering talents, an 1% increase in spell crit chance will result in a gain of 0.5% of a spell's base damage, whereas a 1% increase in spell hit chance will give a 1% increase of a spell's base damage. As long as no other effects come into play, +spell hit rating is more effective than +spell crit rating. But although increasing +spell hit over 99% is not a complete waste if using binary against a resist chance (since in that case the resist chance works as a reduction of the hit chance), in general a 99% spell hit chance will be sufficient for most casters.
If a Mage has taken the Ice Shards or Spell Power talent to increase the crit damage to 200%, hit and crit are basically equal, similar to the situation as it exists with physical damage. Other classes have similar "increase critical strike damage by 50%" talents. 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.
Another important factor to consider are the many effects which can proc from spell crits. These include a warlock's 
[Improved Shadow Bolt], shamans and paladins saving mana on spell crits, and holy spec priests and shamans proccing an armor buff on heal crits (see Inspiration).
For many shadow priests, +spell crit rating on gear is considered to be of very little help. The normal rotation of damage spells used by a shadow priest contains only two, 
[Mind Blast] and 
[Shadow Word: Death], that are capable of a critical, and both have lengthy cooldowns that make continual use impossible – and Shadow Word: Death being used at the end of a battle means that any critical effect is generally wasted. As such, +spell crit rating is one of the least valued gear attributes for many shadow priests, although that is not to say that it has no use (particularly for priests that choose the [Shadow Power] talent). Added +spell hit can be very helpful to shadow priests, however, especially in PvE boss fights or for shadow priests that have not invested in the 
[Shadow Focus] talent.
For dedicated healers, +spell hit rating is essentially worthless. Spells cast on friendly targets (such as heals, buffs, and dispels/cures) always hit. However, +spell crit rating improves the chance of getting a critical effect on helpful and harmful spells alike. Although it is not advisable to rely on the extra healing granted by critical effects from healing spells, a lucky critical heal in a fight going badly could mean the difference between life and death for a group member, or even the entire group. Even if a critical heal results in an overheal, this extra healing has no impact on the threat generated by the healer. Additionally, there are talents available to priests and shamans which grant a short-duration armor buff to the recipient of a critical heal. When given the choice between +spell hit rating and +spell crit rating, a primary healer will always benefit from more +crit, while they will see little if any benefit from +spell hit rating. Just to be clear, if an item says "Improves spell critical strike rating", it will also improve the crit chance of healing spells.
Paladins also have the 
[Illumination] talent, which gives them back 60% mana of the healing spell they crit on. Since this essentially amounts to an average reduction in mana costs for a paladin healer, it's common for paladins to stack +spell crit rating, and find themselves in the area of 25% crit chance.
See also
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