Spell Hit and Spell Penetration

A conversation on my guild’s forums got me curious as to how spell hit and penetration work, so here are some major points from the always-informative WoWWiki concerning these two spell mechanics.

With spell hit and spell penetration, we’re dealing with two different mechanics.

Let’s start with spell hit: This is your base chance to hit depending on level difference. Here’s the chart:

Difference = Chance in PvE

– 3 = 99%

– 2 = 98%

– 1 = 97%

0 = 96%

+ 1 = 95%

+ 2 = 94%

+ 3 = 83%

+ 4 = 72%

+ 5 = 61%

What are the ways to increase spell hit?
* Draenei’s Heroic Presence increases party hit by 1%
* 1% chance to hit for every 12.6 points of spell hit rating
* Various class talents that will boost spell hit

If we look at a boss who is 3 levels higher than the caster, then we have a base chance to hit of 83%.

If we use a balance druid as our example, he might have the following:
83% base chance
4% from Balance of Power talent
3.96% (50 hit rating) from gear
Total = 90.96% chance to hit

Resistance affects hit chance, too, and you can calculate it like this:

(Base chance + Increased chance from gear & talents) * Resistance

For example, if a balance druid attacks a mob 3 levels higher than him or her, uses a binary spell (which has both damage and non-damage effects, like Entangling Roots), and that mob resists 50% spell damage, then the caster’s chance to hit drops to 45.48% (90.96%*50%). A non-binary spell, like Wrath, can be partially resisted based on a second calculation that rolls after spell hit is determined.

As is evident, then, resistance plays a role in hit chance and so that’s where spell penetration comes in. Penetration reduces the target’s resistance to your spell, so increasing this stat should be helpful in this respect.



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