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:

Level
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.

Sources:
http://www.wowwiki.com/Spell_hit_rating
http://www.wowwiki.com/Spell_penetration
http://www.wowwiki.com/Resistance

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