How does Armor Rating work in Dragon Age: Inquisition?

Solution 1:

For the player, armor reduces the damage taken by physical attacks by 2 for every armor point in the campaign, or by 1 in multiplayer.

Armor on monsters reduces the damage taken by 1 per point.

Armor is applied after damage multipliers (like %-Attack, Crit, etc.) but before damage reduction from % melee defense.

The formulas for damage taken are:

For monsters: [WeaponDmg * (1 + Attk%) * (1 + CritDmg%) * (1 + FlankDmg%) * (1 + BarrierDmg%) * (1 + GuardDmg%) - Armor *(1 - ArmorPen%)] * AbilityMultiplier%

For the player: [BaseDmg * (1 + CritDmg%) * (1 + FlankDmg%) - Armor * 2(only in solo mode) *(1 - ArmorPen%)] * (1 - Defense%) * (1 - ElementalDef%)

Source: http://dragonage3.wiki.fextralife.com/Attributes