(This is something that initially confused the hell out of me, and I've been asked about it a few times by friends/guildies. The topic came up on Twitter this morning so I thought I'd do a quick info post about it.)
One of the earliest talents in the Frost DK tree is Nerves of Cold Steel, which grants an exceptional +3% Hit with one-handed melee weapons, as well as increasing the damage of our offhand weapon.
However, there's a lot of confusion about this 3% bonus, how much actual Hit we need in total, and just about Hit in general for Frost DKs.
First, some numbers. Our hit cap for special melee strikes is 8%. This is the number we want to reach and the only Hit number that matters. Our SPELL and AUTOATTACK hit caps are much higher and are not worth chasing.
There's various reasons, but the simple explanation is that we will do more DPS with other secondary stats (Mastery, Crit, Haste) than with extra Hit. Is surplus Hit wasted? Nope. But it's just not optimal.
So we want 8% Hit total. But is that in addition to the 3% from Nerves of Cold Steel? Or including it? How much total should our character sheet say...5%? 8%? Or even 11%?
The answer: We want our in-game character sheet to say 8% Hit.
Our sheet already includes the 3% bonus from Nerves of Cold Steel (meaning that we need to get 5% from gear). It's quite simple to test and verify this. Simply remove all of your gear except your weapons and look. You'll have 3%, plus whatever +Hit your equipped weapons give you.
(You have to have one-handed weapons equipped because Nerves specifically grants you the bonus ONLY with one-handers. If you try this with no weapons your sheet will say 0%.)
My DK with no gear except two vendor cutlasses (and a tabard for dignity).
Nice and simple? Well, almost. To make this even MORE confusing, our official WoW Armory character sheets do NOT include the 3% Hit bonus. So keep that in mind if you're checking out the Armory and getting confused, or if someone points out that you're not hit capped. Be aware that the info can differ depending on where your character is being viewed.
Here's an example of a side-by-side comparison of my DK's in-game character sheet and Armory page, taken at the exact same time. (The difference in Speed is because I am in Unholy Presence in-game, something else not calculated by the Armory.)