Armor

Armor is an attribute shared by all units. It reduces the amount of physical damage a unit takes, but can also increase the amount of damage a unit takes. The amount of damage a unit takes gets reduced if its armor value is positive, and increased if the armor value is negative. Armor is increased by Agility, certain spells and when you obtain items that increase armor.

Damage Reduction/Increase
Each point of armor reduces incoming physical damage. The formula used to determine the amount of damage reduced is as follows:
 * Damage Reduction = (0.06 * armor) / (1 + 0.06 * armor)

Each point of negative armor increases incoming physical damage. The formula used to determine the amount of damage increased is as follows:
 * Damage Increase = 1 - (1/0.94)^(armor)

Negative armor has a cap of -20 (71% damage increase). Further reducing the armor will not change the damage increase.

Armor Stacking
It is generally conceived that armor gets less and less effective the more you have (since the extra damage reduction gets less and less). That a Plate Mail gives you less extra protection from attacks if you already have 20 armor than if you would have only 5. This is false. If one Plate Mail makes the hero survive 3 extra attacks, then 4 Plate Mails will make the hero survive a total of 12 extra attacks before dying. Each Plate Mail gives the same amount of extra protection, which is in this case 3 more attacks before dying.

Proof: Consider a hero with 1000 hp and 0 armor. To kill it one needs to deal at least 1000 damage to it.

If we give the hero 10 armor, which is 37.5% damage reduction, every attack would only deal 62.5% of the original value (100% - 37.5% = 62.5%). To kill it now, one needs to deal 1600 damage (1600 * 0.625 = 1000). You could say that the hero now have 600 more effective hp (EHP).

If we instead give the hero 20 armor, which is 54.5% damage reduction. The damage multiplier is now 45.5%. The damage needed to kill would increase to 2200 (2200 * 0.455 = 1000). The increase in EHP is 1200, twice the amount as given by only 10 armor.

Every armor point adds an additional 6% of your maximum HP to your EHP.

List of items

 * Ring of Protection +2 Armor
 * Chainmail +5 Armor
 * Helm of Iron Will +5 Armor
 * Platemail +10 Armor
 * Ring of Basilius +1 Armor
 * Buckler +5 Armor
 * Medallion of Courage +6 Armor
 * Mekansm +5 Armor
 * Veil of Discord +5 Armor
 * Armlet +5 Armor
 * Blade Mail +5 Armor
 * Shiva's Guard +15 Armor
 * Assault Cuirass +10 Armor
 * Helm of the Dominator +5 Armor
 * Satanic +5 Armor