Armor



Armor is a stat that reduces (or increases, if negative) physical damage a unit takes from spells and attacks. Every unit is capable of gaining or losing armor, and most units start with a small amount of base armor, some even starting with negative armor. A hero's armor can be passively increased with, certain items, talents and some abilities. Armor of any unit can also be temporarily increased or reduced with some abilities.

Each point of increases a hero's armor by  or $$\tfrac{1}{6}$$.

Total armor is defined as



With  being the index of Armor,   being the index of Main Armor,   being the index of Armor Negating Multiplier and   being the index of Bonus Armor (Armor values from other than  sources).

Base Armor
Base armor is the part of the main armor that never changes throughout a game. It consists of one fixed value set for each unit individually. The base armor of a unit can be a negative number. Since only heroes have agility, the HUD of all non-hero units shows their base armor.

Main Armor
Main armor is the armor value shown in white numbers near the shield icon in the HUD, consisting of base armor and the armor granted by a hero's agility. The only way to improve a hero's main armor is to increase its, which is gained by leveling up, acquiring certain items, or with the help of certain abilities.

The main armor is defined as



With  being the index of Main Armor,   being the index of Base Armor and   being the index of the hero's level.

Bonus Armor
Bonus armor is the armor value shown in green numbers with a plus on the left, right below the white armor number on a unit's statistics. Whenever an armor granting item or armor increasing ability shows a, e.g.   , it increases the bonus armor of the affected unit.

Probably the most important difference between main and bonus armor is that illusions only benefit from main armor, although their HUD still shows the bonus armor just like on other heroes, to make them less obvious to the enemy. Some abilities like and  also only affect main armor.

Modifying Armor
A lot of abilities and items have abilities that grant or reduce armor. These changes always affect bonus armor, and never added to the main armor.

Armor Increasing Abilities
The following abilities increase armor:

Armor Reducing Abilities
The following heroes have a talent that causes their attacks to reduce armor of the attacked target. This is also known as Armor Corruption.

The reduction lasts 10 seconds. Multiple sources of Armor Corruption do not stack.

The following abilities reduce armor:

Armor Negating Abilities
Some abilities negate a unit's armor by reducing or increasing armor based on the unit's armor, effectively removing a percentage of the armor on the target. This Armor negation only affects the armor value of units, their armor type is unaffected and still reduces damage normally.

The following abilities negate armor:

Armor Granting Talents
The following heroes have a talent that grants them bonus armor.

Besides these, the following heroes have talents which increase the armor of the units they summon

Damage Multiplier
All units, including buildings, have an inherent base armor value and armor type. Any physical damage dealt to a unit is multiplied by the damage multiplier, resulting in either damage reduction or increase depending on the target's armor value.

For any real-valued armor, the damage multiplier is defined as

With  being the index of Damage Multiplier and   being the index of Main Armor.

The damage multiplier limits are and, for infinitely negative and positive armor, respectively.
 * Examples

Effective HP
The total amount of physical damage a unit can take due to the armor it has is known as effective HP (or EHP). 16.66 armor adds 100% to EHP. This means a unit with 1000 health and 16.66 armor can take 2000 physical damage. The formula adds 6% EHP per point of armor regardless of the previous armor value.

However, EHP value is of a diminished benefit as a player gaining 1 armor from 0 armor would increase EHP from 100% to 106%, while a player gaining 1 armor from 50 armor would increase EHP from 400% to 406%. On the other hand, the effectiveness of armor is much lower at negative values (refer to graph). Total EHP trends downwards towards 50%, meaning a unit with 1000 health and infinitely low armor would still be able to take 500 physical damage. At this point, losing or gaining 1 armor has essentially no effect.

This definition of EHP assumes all damage taken is physical. EHP against magical damage (such as 's or 's ultimate) is modified by magic resistance.

Effective HP against physical damage is defined as



With  being the index of Current Health and   being the index of Damage Manipulation.


 * Example 1:


 * A Level 25 has a total health of  and  points of armor. What is his effective HP against physical damage?






 * 's effective HP against physical damage in this example is.


 * Example 2:


 * The same Level 25 from previous example (has a total health of ) is affected by a Level 3, and his armor is now . What is his effective HP against physical damage?






 * 's effective HP against physical damage in this example is.

Armor Types
There are several different types of armor, which determine how much damage a unit takes against certain attack damage types. Each of the 3 different armor types either reduces, increases or does not affect the damage from each of the damage types, on top of armor values manipulating them.

Attack damage dealt against armor type is defined as



With  being the index of Attack Damage,   being the index of Damage Multipler and   being the index of Armor Type Multiplier.

This table shows how much damage each armor type reduces against each attack damage type and which unit uses which armor type (units which take a set amount of damage per attack are excluded).


 * Example 1:
 * with 100 damage attacks a siege creep which has 0 armor and deals 50 damage to it. The attack type "hero" deals 50% less damage against the armor type "structure" which is the siege creeps' and all buildings' armor type. If the siege creep gained 5 armor, how much the 100 damage attack would deal?


 * Siege Creep's Base Armor for this example is.
 * Siege Creep's Base Armor for this example is.




 * The siege creep damage multiplier is undefined.




 * The armor type multiplier is 0.5 because the attack type "hero" deals 50% less damage against the armor type "structure".
 * Therefore in this example, 's 100 damage attack to the siege creep with 5 armor would be . The same attack would deal damage to a unit with any other armor type, since attack type hero deals full damage to them.

Trivia

 * In DotA the base magic resistance was bound to the assigned armor. In case of Hero Armor only 75% of the magic damage was applied. Some heroes possessed hidden passive skills to alter their base magic susceptibility albeit Hero Armor to 90% or 65% . Nowadays, in Dota 2 magic resistance works independently from armor.
 * In 6.86 Armor types were renamed and some other types were removed.
 * The following armor types were renamed: Unarmored ➜ Soft, Light ➜ Weak, Medium ➜ Basic, Heavy ➜ Strong and Fortified ➜ Structure.
 * Weak and Basic armor types were removed. Units who previously uses the Weak and Basic armor type now use the Soft and Strong armor type respectively.

Negative Armor Disparity
Amplified damage from negative armor is calculated differently in WC3 DotA than in Dota 2.

Negative armor in WC3 DotA has a cap of -20 armor (71% damage increase). Further reducing the armor does not change the damage increase. Also, the more aggressive damage amplify formula is used resulting in a max damage increase of 71%.

The amplified damage is defined as



With  being the index of armor.

 Comparison table