- For a list of hero armor values, see the Table of Armor Values
Armor is used to reduce the physical damage taken by a unit. Armor consists of two parts: armor type and armor value. A combination of these two factors is used to determine the damage reduction. The armor type of a unit is fixed while the armor value can be increased using by items, increasing a hero's Agility, or by abilities.
The damage reduction for positive armor values is calculated using the following formula:
- Damage Reduction = (0.06 × Armor) ÷ (1 + 0.06 × Armor)
It is possible to achieve a negative armor value. The resulting amplification of physical damage mirrors the damage reduction of positive armor, and is calculated using:
- Damage Increase = (0.06 × |Armor|) ÷ (1 + 0.06 × |Armor|)
These two formula can be combined:
- Damage Taken = 1 - ±(Armor) × (0.06 × |Armor|) ÷ (1 + 0.06 × |Armor|)
There is no limit to the maximum or minimum armor value.
Each unit or structure has a fixed armor type which cannot be changed. The types of armor and their damage interactions are listed below.
|Attack Type||Armor Type|
|Basic Armor||Fortified Armor||Hero Armor|
- For a comprehensive list, see the Table of Armor and Damage Types
Fortified armor is used by buildings and siege creeps. It is one of the sturdiest types of armor, but is weak against siege attacks. It has decent defense against basic attacks, and great defense against piercing attacks and hero attacks.
Hero armor is used by heroes and a few special summons. It has decent defense against basic attacks and siege attacks, and great defense against piercing attacks.
Effective Hit Points
The Effective Hit Points, (or EHP), of a hero is the amount of damage a hero is able to sustain (before damage reductions). From this, it can be concluded that each extra point of armor increases the EHP of a hero by a constant 6%. This allows heroes survivability to grow exponentially with armor. By contrast, strength or raw HP items scale linearly. This is one of the main reasons why Agility heroes scale well and are often more survivable than Strength heroes late game. This observation briefly popularized Slardar and Dazzle.
Negative Armor Strategies
Armor reduction is one of the most effective ways of killing tanky lategame agility heroes. These heroes are often reliant on their high armor to give them high EHP and survivability. This observation lead to the brief popularity of negative armor strategies at the pro-level during the Warcraft III Dota era. These strategies often combined heroes such as Slardar and Dazzle (whose ultimates can both go through Black King Bar) to reduce total armor by up to 40, creating a reasonably effective anti-carry strategy.