Armor

Only physical abilities (not bleeds nor spells) get a reduction from armor. The armor value is specific to each unit (player, mob or boss); for instance, the armor of lvl93 bossess is 24835.

The armor reduction is computed like so:
DR = armor / (armor + armor_parameter)
armor_parameter = (level * a) - b
Where ‘a’ and ‘b’ are dependant on the attacker’s level; for level 86 and up a=4037.5 and b=317117.5, so the reduction in a mop raid would be:
armor_parameter = 90 * 4037.5 - 317117.5 = 46257.5
DR = 24835 / (24835 + 46257.5) = 0.3493
Which means physical attacks will get reduced by 34.93%. In ShadowCraft, we use (1 – DR) as a multiplier:
reduced_damage = base_damage * (1 - DR)

As a reference, this is the factor for a cata raid:
11977 / (11977 + 85 * 2167.5 - 158167.5) = 11977 / (11977 + 26070) = 0.3148