Spell hit

Spell hit is an attribute that increases a caster's chance to hit with offensive spells (healing abilities never miss, and are not affected by spell hit chance). Spells that fail to hit are shown as a "miss", and have no effect on their target.

With the removal of hit and expertise from gear, players automatically have a 100% chance to hit creatures up to and including 3 levels above the attacking character. However, if players attempt to attack targets 4 or more levels above their character level, their spells may still miss, as shown in the table to the right.

For example, if a level 90 character attacks a level 93 target, the spell will hit. However, if the same level 90 character attacks a level 94 target, spells have an 11% chance to miss.

Previous calculations
Chance to hit with a spell depends on the level difference between the caster and the target, as well as whether the target is a player or not. For example, a spell cast by a level 80 player (with no gear or spell hit-modifying effects) will have an 85% chance to hit a level 83 monster, and a 94% chance to hit a level 82 player. Players many levels below their target will always have at least a 1% chance of landing a spell.

Stats increasing spell hit chance (hit rating, expertise rating, and Spirit) are commonly found on high-level gear, gems, and enchants, and can be gained temporarily from food and elixir buffs. Additionally, the following racial abilities can increase the player's spell hit chance by 1%: Note that the Dwarf racial Crack Shot does not include wands, although the tooltip may suggest otherwise.

With a high enough total of hit rating, expertise rating and spirit (where applicable as mentioned above), a player's chance to hit with spells can reach 100%. Players receive no additional benefit from having more than 100% chance to hit a target.

For the purposes of spell hit chance, expertise rating is equivalent to hit rating, and for balance druids, mistweaver monks, elemental shaman, and shadow priests, so is Spirit. A total of 340 of those three attributes, in any combination, will increase spell hit chance by 1% at level 90.

PvE spell hit cap
In end-game PvE content, monsters and bosses are at most 3 levels above the player, so having more than 15% spell hit is unnecessary; in heroic dungeons, monsters and bosses are at most 2 levels above the player, so having more than 12% spell hit is unnecessary. If you're affected by one of the racial abilities described above, you can reduce these requirements by 1% to find out how much spell hit chance you need from the hit rating, expertise rating, and Spirit stats to ensure that your spells never miss.

Spell hit rating increases spell hit linearly. For example, at level 90, you need 340 hit rating to increase spell hit by 1%, and 680 hit rating to increase spell hit by 2%. For the amount of hit/expertise rating or Spirit required to increase spell hit chance by 1% at lower levels, consult the table below: You can only again an integral amount of spell hit from gear, so if you'd like to ensure that your spells never miss, round the required amount of hit rating up to the nearest integer. For example, to get 15% spell hit chance required at to avoid missing Burning Crusade raid bosses at level 70, you'd need  hit rating, so having 394 ensures that your spells won't miss, while having 393 hit rating makes   of your spells miss.