The Bane of us math-tankadins, what is the number on miss?
Well, I found a formula on maintankadin/elitistjerk, and the conlusion seems to be:
540 defense will give you a little bit more then 4% miss, but use 4% to be safe.
every 5 defense ontop of 540 will give you ~ 0.09% extra miss
so my current 554 defense will give: 4% + 14/5 * 0.09 = 4,25% miss
The tooltip says it's 6.16%, so that's almost a 2% difference.
Luckily in raids you should have some buffs on you like kings and MotW, which will give you around 1% more avoidance (not counting totems, because they can disappear if the shammy dies)
So a formula would be something like: (for raids)
That means my unhittability lies at 101.61%, that's 0.8 under blockcap..mmm
Time to run through my bank for some other gear :p