# Armor penetration

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Armor penetration is a champion statistic that allows the champion to ignore some or all of a target's armor. All champions have 0 base armor penetration but can increase it with items, runes, masteries and some champion abilities. This cannot affect enemy armor beyond 0 to deal bonus damage.

Armor reduction is the effect of some items and champion abilities that temporarily reduces the armor of one or more targets. This allows allies to benefit from the reduction of armor. This can reduce armor below 0, resulting in bonus damage (see Armor).

## Order of calculations

When attacking, armor penetration and armor reduction are considered in the following order [1]:

1. Armor reduction, flat
2. Armor reduction, percentage
3. Armor penetration, percentage
4. Armor penetration, flat

## Flat armor reduction

The target's armor is reduced by an amount. Flat armor reduction stacks additively.

Example: 20 armor reduction reduces the target's armor by 20, so a target with 30 armor will be reduced to 10 armor (30 − 20 = 10).

Flat armor reduction can reduce a target's armor below zero. For example, if an enemy with 10 armor has their armor reduced by 25, the enemy will have −15 armor.

## Percentage armor reduction

The target's armor is multiplied by a percentage (100% − the listed reduction). Percentage armor reduction stacks multiplicatively and is ignored if the target's armor is 0 or less.

Example: 20% armor reduction multiplies the target's armor to 80%, so a target with 30 armor will be reduced to 24 armor (30 × 0.8 = 24).

Percentage armor reduction makes a bigger difference on targets with higher armor. For instance, with 40% armor reduction, a target with 200 armor will lose 80 while a target with only 50 armor will lose 20.

## Percentage armor penetration

The target's armor is treated as being multiplied by a percentage for purposes of damage calculation (100% − the listed penetration). Percentage armor penetration stacks multiplicatively and is ignored if the target's armor is 0 or less.

Example: 20% armor penetration causes the target to take damage as if its armor was multiplied by 80%, so a target with 30 armor will be treated as though it had 24 for purposes of damage calculation (the target's actual armor value will not change, however).

Because the target's actual armor value does not change, anything else depending on that value also doesn't change (e.g. ).

Percentage armor penetration makes a bigger difference on targets with higher armor. For instance, with 40% armor penetration, a target with 200 armor will be considered as having 80 less while a target with only 50 armor will be considered as having 20 less.

## Flat armor penetration

The target's armor is treated as being reduced by an amount for purposes of damage calculation, but cannot be reduced below 0. Flat armor penetration stacks additively.

Example: 20 armor penetration causes the target to take damage as if its armor was 20 less, so a target with 30 armor will be treated as though it had 10 for purposes of damage calculation (the target's actual armor value will not change, however).

Because the target's actual armor value does not change, anything else depending on that value also doesn't change (e.g.  ).

## Examples

Given 20 flat armor reduction and 30% armor reduction, and the target is affected by 10 flat armor penetration and 35% armor penetration,

• Target A has 80 armor.
• The 80 is reduced to 60 by the 20 armor reduction.
• The 60 is reduced to 42 by the 30% armor reduction.
• The 42 is considered to be 27.3 by the 35% armor penetration.
• The 27.3 is considered to be 17.3 by the 10 armor penetration.
Target A takes damage as if it has 17.3 armor.
• Target B has 18 armor.
• The 18 is reduced to −2 by the 20 armor reduction.
• The −2 is not affected by any further calculations because it is less than 0.
• Target B takes damage as if it has −2 armor.

Graph of the % increase in physical damage with apen vs no apen:

## Increasing armor penetration

### Items

• : Unique passive: +35% armor penetration. +40 attack damage. 2300 gold.
• : Unique passive: +10 armor penetration. +25 attack damage. Unique passive: +10% cooldown reduction. 1337 gold.
• : Unique passive: +20 armor penetration.+30 attack damage; +15% critical chance; +10% cooldown reduction. Unique active: Gain +40% attack speed and +20% movement speed for 6 seconds (4 seconds for ranged champions) - 45 second cooldown. 2700 gold.
• : Unique passive: +10 Armor Penetration.+200 health, +50 attack damage, +10% Cooldown Reduction. Unique passive: Dealing physical damage to an enemy champion reduces their Armor by 5% for 4 seconds. This debuff stacks up to 5 times. 3000 gold.

### Champion abilities

Note: Only the armor penetration effect of these abilities is shown here, to read more information on each of these abilities, follow the link on each of them.

• passively grants him 5 / 10 / 15 / 20 / 25% armor penetration.
• upon activation grants him 50% penetration to bonus armor.

### Masteries

• grants 2 / 4 / 6% armor penetration.

## Reducing armor

### Items

• : Unique passive: Dealing physical damage to an enemy champion reduces their Armor by 5% for 4 seconds. This debuff stacks up to 5 times.+200 health, +50 attack damage, +10% Cooldown Reduction. Unique: +10 Armor Penetration. 3000 gold..

### Champion abilities

Note: Only the armor reduction effect of these abilities is shown here, to read more information on each of these abilities, follow the link on each of them.

Percentage Reduction:

• reduces the armor of all enemies hit by 10 / 14 / 18 / 22 / 26% for 3 seconds.
• reduces the armor and magic resistance of the enemy hit by his first attack after cast, by 10 / 15 / 20 / 25% for 5 seconds
• reduces the armor of enemies hit by her autoattacks by 3% for 5 seconds. This debuff stacks up to 5 times.
• reduces the target's armor and magic resistance by 20 / 22 / 24 / 26 / 28% for 4 seconds.
• , when empowered by having more than 50 Fury, Dice will reduce the armor of all enemies hit by 15 / 20 / 25 / 30 / 35% for 4 seconds.
• reduces the armor of his target by 20% and gains for the same amount. This amount is doubled over the next 4 seconds. The armor reduction lasts for another 4 seconds after the drain completes.
•  reduces the armor of all enemies hit by 12 / 14 / 16 / 18 / 20% for 5 seconds.
• reduces the target's armor by 20% for 4 seconds after every third consecutive hit.
• reduces the armor of the target hit by 10 / 15 / 20 / 25 / 30% for 3 seconds.
• reduces the armor of targets hit by his basic attacks or by 15% for 3 seconds. Only one target may be challenged at a given time.

Flat Reduction:

• fires automatically every half second, reducing enemies armor with each hit by 1 / 2 / 3 / 4 / 5 for 2 seconds up to a maximum of 8 stacks, 8 / 16 / 24 / 32 / 40.
• reduces the armor of all enemies in the area by 20 / 25 / 30 / 35 / 40 for the time they are on it plus 1 second.
• reduces the target's armor by 10 / 15 / 20 / 25 / 30 for 1.25 / 1.5 / 1.75 / 2 / 2.25 seconds.
• reduces the armor of all enemies hit by its activation damage by 5 / 10 / 15 / 20 / 25 (+ 5% armor) for 4 seconds.

## Notes

• Armor penetration is a very valuable stat for physical damage dealing champions. There are few sources for it, so armor penetration Marks and Quintessences are very popular runes.
• Armor penetration benefits all sources of physical damage including all champion abilities that deal physical damage.
• For example, will benefit from armor penetration as it deals physical damage, however his will not benefit from armor penetration as it deals magical damage.
• The items that deal on-hit physical damage:, , ,  and , will also benefit from Armor Penetration.

## Start a Discussion Discussions about Armor penetration

• #### Efficiency of Last Whipser

7 messages
• It is not so easy to compare the efficiency of items as such tho. Say you bought a PD as first item (that is an assumption, I know it sucks...
• It's very difficult to generate a general efficiency curve for Last Whisper because it is based on so many variables.  It's heavily dependent...
• #### Interaction between Armor/Magic Resistance reduction and percentage bonus stat buff.

5 messages
• Remember that this was tested on S3, so what follow might be incorrect. Here is a copy of what I posted on reddit a month ago to explain the i...
• Hmm I didn't think of the possiblity it could be like that.  That would be crazy as hell if the armor amount reduced by % reduction were fi...