Why 490 Defense is Mandatory

The Defense Magic Number - 490

In The Burning Crusade, it's necessary for any Paladin or Warrior to have 490 Defense, absolute minimum. Why 490?

Raid bosses are level 73. In order for a mob to have the minimum base chance of critting you (5%), you must have Defense equal to 5 times the mob's level (ie, you need to have maxed defense as if you were that level). That's 365 Defense.

Now, every 25 Defense skill reduces the chance to crit and hit, and increases the chance to dodge, parry, or block by 1%. Therefore, in order to reduce chance to crit by 5%, you will need to get an additional 125 Defense. That's a total of 490 Defense.

There are a few exceptions. Teremus the Devourer has a higher than 5% crit rate for some reason, so he'll still crit you sometimes. Just not often. Malicious Instructors do this too. This also applies to any NPC with an Unbalancing Strike. Fortunately, they're few and far between.

So there you go. 490 Defense makes you (effectively) uncrittable by level 73 mobs.