What is the formula for armor/magic resist reduction?

As far as I can tell, it's something like this:

damage reduction = armor / (armor + 100)

Is this accurate?


Yes, that's correct. The calculations are:

Armour Resist: Damage Reduction = Total Armor / (100 + Total Armor)

Magic Resist: Damage Reduction = Total Magic Resistance / (100 + Total Magic Resistance)