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Armor penetration

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Armor penetration is a champion statistic that directly reduces armor, meaning 10 armor penetration makes a target have -10 armor or 20% penetration equals 20% less. The difference between penetration and armor reduction is that reduction can reduce armor below zero (the same is true for magic), which means attacks deal more than 100% of damage to it.

All champions have 0 base armor penetration but can increase it with items, runes, masteries and some champion abilities.

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 reduction applies to base armor and bonus armor separately.[2] For example, 30% armor reduction would reduce both base armor by 30% and bonus armor by 30% (see reference for example). This means it retains multiplicative stacking with Last Whisper item.png Last Whisper and derivatives' bonus armor penetration.

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. Rammus Rammus's Spiked Shell.png Spiked Shell).

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. Rammus Rammus's Spiked Shell.png Spiked Shell).

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.

Increasing armor penetration

Items

  • Last Whisper item.png Last Whisper: Unique Passive – Last Whisper: +30% bonus armor penetration. +25 attack damage. 1300 Gold.
  • Lord Dominik's Regards item.png Lord Dominik's Regards: Unique Passive – Last Whisper: +45% bonus armor penetration. +40 attack damage. Unique Passive – Giant Slayer: Grants up to +15% physical damage against enemy champions with greater maximum health than you (+1.5% damage per 50 health difference, maxing at 500 health difference). 2700 Gold.
  • Maw of Malmortius item.png Maw of Malmortius: +10 armor penetration. +55 attack damage, +50 magic resist. Unique Passive – Lifeline: Upon taking magic damage that would reduce health below 30%, grants a shield that absorbs 300 + (100% bonus MR) magic damage for 5 seconds (90 second cooldown). Unique Passive – Lifegrip: When Lifeline triggers, gain +25% attack speed, +10% spell vamp, and +10% life steal until out of combat. 3250 Gold.
  • Mortal Reminder item.png Mortal Reminder: Unique Passive – Last Whisper: +45% bonus armor penetration. +40 attack damage. Unique Passive – Executioner: Physical damage inflicts Grievous Wounds icon Grievous Wounds on enemy champion for 5 seconds. 2700 Gold.
  • Serrated Dirk item.png Serrated Dirk: Unique Passive: +10 armor penetration. +20 attack damage. Unique Passive: After killing any unit, your next basic attack or single target spell deals +15 bonus damage. 1100 Gold.
  • Youmuu's Ghostblade item.png Youmuu's Ghostblade: Unique Passive: +20 armor penetration. +65 attack damage, +10% cooldown reduction. Unique Active: Grants +20% movement speed and +40% attack speed for 6 seconds (45 second cooldown). 3200 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.

Masteries

  • Devastating Strikes mastery s4.png Battering Blows grants 1.4 / 2.8 / 4.2 / 5.6 / 7% armor penetration.
  • Arcane Knowledge mastery s3.png Precision grants 0.6 / 1.2 / 1.8 / 2.4 / 3 flat + 0.06 / 0.12 / 0.18 / 0.24 / 0.3 per level armor penetration.

Runes

Name Type Tier 1 (Lesser) Tier 2 (Normal) Tier 3 (Greater)
Armor Penetration Mark

GMarks (1)

0.72

5 IP

1

35 IP

1.28

410 IP

Seal X X X
Glyph X X X
Quintessence

GQuintessences (1)

1.42

15 IP

1.99

100 IP

2.56

1025 IP

Hybrid Penetration

(Armor Penetration / Magic Penetration)

Mark

GMarks (1)

X X 0.9 armor penetration
0.62 magic penetration

820 IP

Seal X X X
Glyph X X X
Quintessence

GQuintessences (4)

X X 1.79 armor penetration
1.4 magic penetration

2050 IP

Reducing armor

Items

  • The Black Cleaver item.png The Black Cleaver: Unique Passive: Dealing physical damage to an enemy champion Cleaves them, reducing their armor by 5% for 6 seconds (stacks up to 6 times, up to 30%). +300 health, +55 attack damage, +20% cooldown reduction. Unique Passive – Rage: Dealing physical damage grants 20 movement speed for 2 seconds. Assists or kills on Cleaved enemy champions or kills on any unit grant 60 movement speed for 2 seconds instead. This movement speed bonus is halved for ranged champions. 3500 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:

  • Jarvan IV Jarvan IV's Dragon Strike.png Dragon Strike reduces the armor of all enemies hit by 10 / 14 / 18 / 22 / 26% for 3 seconds.
  • Jayce Jayce's Transform- Mercury Cannon.png Transform: Mercury Cannon reduces the armor and magic resistance of the enemy hit by his first attack after cast, by 10 / 15 / 20 / 25% for 5 seconds
  • Kayle Kayle's Holy Fervor.png Holy Fervor reduces the armor of enemies hit by her autoattacks by 3% for 5 seconds. This debuff stacks up to 5 times.
  • Kog'Maw Kog'Maw's Caustic Spittle.png Caustic Spittle reduces the target's armor and magic resistance by 12 / 16 / 20 / 24 / 28% for 4 seconds.
  • Renekton Renekton's Slice.png Slice and Dice, 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.
  • Sion Sion's Roar of the Slayer.png Roar of the Slayer reduces the armor of the first target hit by 20% for 2.5 seconds.
  • Trundle Trundle's Subjugate.png Subjugate 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.
  • Urgot Urgot's Noxian Corrosive Charge.png Noxian Corrosive Charge reduces the armor of all enemies hit by 12 / 14 / 16 / 18 / 20% for 5 seconds.
  • Vi Vi's Denting Blows.png Denting Blows reduces the target's armor by 20% for 4 seconds after every third consecutive hit.
  • Wukong Wukong's Crushing Blow.png Crushing Blow reduces the armor of the target hit by 10 / 15 / 20 / 25 / 30% for 3 seconds.
  • Xin Zhao Xin Zhao's Challenge.png Challenge reduces the armor of targets hit by his basic attacks or Audacious Charge.png Audacious Charge by 15% for 3 seconds. Only one target may be challenged at a given time.

Flat Reduction:

  • Corki Corki's Gatling Gun.png Gatling Gun 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.
  • Nasus Nasus's Spirit Fire.png Spirit Fire 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.
  • Rammus Rammus's Puncturing Taunt.png Puncturing Taunt reduces the target's armor by 10 / 15 / 20 / 25 / 30 for 1.25 / 1.5 / 1.75 / 2 / 2.25 seconds.
  • Taric Taric's Shatter.png Shatter 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.

References

Start a Discussion Discussions about Armor penetration

  • Efficiency of Last Whipser

    11 messages
    • Modified the post to take into account the comments above. Clarified the paragraph about abilities with 100% AD ratios. Removed the comment ab...
    • LW is a DPS multiplier. Your DPS is a product of Attack Damage, Attack Speed, Crit variables, and enemy resistance. With LW, you could say ...
  • Penetration

    4 messages
    • Oh thanks a lot, It makes sense to me
    • Nice, I understand it too.

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