I'm trying to compare armor value as a stat to something like dodge. Moceran is my tank.
Moceran's effective health pool sitting in his own gear with his own buffs is 30574 / (.85 * .3745 * .48) Or 200,096 EHP. ( I ignored blocks, because... Too much math to include them)
This is his HP divided by damage taken through mitigation buffs and talents, armor mitigation, and avoidance.
15.2796% is how much damage gets through to me on your average swing.
Boss hits for 80k (This is about the level of hard hitting Ulduar bosses I think)
After ignoring all factors besides armor, such as avoidance or mitigation buffs.
I would take 29960 damage as I am with 25442 armor(62.55% mitgation).
I would take take 30816 damage with 24314 armor(61.48% mitgation).
That's 856 damage per swing that we can count on just not happening. For an extra 1128 armor. Since armor mitigation is the first thing calculated, I can count on taking at least 1.07% less damage. To get the same mitigation from dodge would require about 67 dodge rating. (42 dodge rating = 1.07% dodge. Multiply the damage left after armor mitigation to stay at 1.07% and you get 67)
I feel like I made a few errors somewhere... 1128 seems like a lot of armor to be just as good as 67 dodge.