Death Knights’ Hit and Expertise - sounds cool, what’s it about?

Now as a Death Knight you have to worry about two types of Hit. Spell Hit and Melee Hit. Yes, they are different. Then, if you want to add in a side complication, there is the Melee Hit for DK’s who dual wield (DW).

Melee Hit
Versus a Raid Boss your special attacks (Read: yellow damaging attacks) all have a 9% chance to miss. This is for DW (dual wield) and 2H (two handers) DK’s.
32.79 Hit Rating is equal to 1% Melee Hit
295.11 Hit Rating is equal to 9% Melee Hit (this is the Melee Hit cap)
DW imposes a penalty, requiring 24.6% Melee Hit to reach the Melee Hit cap with white attacks
DW still only has a 9% Melee Hit cap for special attacks

Spell Hit
26.23 Hit Rating is equal to 1% Spell Hit
445.91 Hit Rating is equal to 17% Spell Hit (this is the Spell Hit cap)
Improved Faerie Fire (Balance Druid debuff) or Misery (Shadow Priest debuff) increases your spell hit by 3%, or 78.69 Hit Rating.
Virulence + Misery = 6% spell hit, or 157.38 Hit Rating

So what are the automatic bonuses to Hit for your character?
Unholy Spec: Virulence 3% spell hit
Draenei Racial: Heroic Presence 1% melee/spell hit

In a typical raid environment with Virulence and Heroic Presence you will only need 288.53 Hit Rating to Spell Hit cap, which is less than the 295.11 Hit Rating required to Melee Hit cap.
So what is your Hit Rating cap? Well this is where you have to sit down and do a little figuring on your own. Do you have a SP or Boomkin in your raids? Does your spec include Virulence? Do you get into the same party as a Draenei in a raid? Once you answer those questions, you can find out your hit cap with this information very quickly.

Taken from SkeltonJack