Armor is a stat that all units have, including minions, monsters, and buildings. Increasing armor reduces the physical damage the unit takes. Each champion begins with some armor which increases with level. You can gain additional armor from abilities, items, masteries, and runes. Armor stacks additively.

At level 18, base armor ranges from 61 ( Heimerdinger) to 90 ( Maokai and Poppy).

Damage reduction

Incoming physical damage is multiplied by a factor based on the unit's armor:

Damage multiplier = 100 / (100 + Armor) if Armor ≥ 0

Damage multiplier = 2 − 100 / (100 − Armor) if Armor ≤ 0

Examples:

• 25 armor → ×0.8 incoming physical damage (20% reduction).
• 100 armor → ×0.5 incoming physical damage (50% reduction).
• −25 armor → ×1.2 incoming physical damage (20% increase).

Stacking armor

Every point of armor requires a unit to take 1% more of its maximum health in physical damage to be killed. This is called "effective health."

Example: A unit with 60 armor has 60% of its maximum health in its effective health, so if the unit has 1000 maximum health, it will take 1600 physical damage to kill it.

What this means: by definition, armor does not have diminishing returns, because each point increases the unit's effective health against physical damage by 1% of its current actual health whether the unit has 10 armor or 1000 armor.

Note: Unlike health, increasing armor also makes healing more effective because it takes more effort to remove the unit's health than it does to restore it.

Ways to increase armor

Items

• Aegis of the Legion: +18 armor. Unique Aura: Nearby allied champions gain +12 armor, +8 attack damage, and +15 magic resistance. +270 health, +24 magic resistance. 1925 gold.
• Atma's Impaler: +45 armor, +18% critical strike chance. Unique Passive: You gain attack damage equal to 1.5% of your maximum health. 2355 gold.
• Chain Vest: +45 armor. 700 gold.
• Cloth Armor: +18 armor. 300 gold.
• Doran's Shield: +10 armor, +120 health, +8 health regeneration. 475 gold.
• Emblem of Valor: +25 armor. Unique Aura: Nearby allied champions gain +10 health regeneration. 900 gold.
• Frozen Heart: +99 armor, +500 mana. Unique Passive: +20% cooldown reduction. Unique Passive: Nearby enemies suffer −20% attack speed. 2775 gold.
• Glacial Shroud: +45 armor, +425 mana. Unique Passive: +15% cooldown reduction. 1525 gold.
• Guardian Angel: +68 armor, +38 magic resistance. Unique Passive: Revives your champion upon death, restoring 750 health and 375 mana. 5 minute cooldown. 2600 gold.
• Locket of the Iron Solari: +35 armor, +300 health. Unique Aura: Nearby allied champions gain +15 health regeneration. Unique Active: Shield yourself and nearby allies for 5 seconds, absorbing up to 50 damage, +10 per level. 60 second cooldown. 2225 gold.
• Madred's Bloodrazor: +25 armor, +40 attack damage, +40% attack speed. Unique Passive: On hit, target suffers magic damage equal to 4% of target's maximum health (maximum 120 versus monsters). 3800 gold.
• Madred's Razors: +23 armor, +15 attack damage. Unique Passive: On hit, 20% chance for target minion/monster to suffer 300 magic damage. 1000 gold.
• Ninja Tabi: +25 armor Unique Passive: Enhanced Movement 2. Reduces the damage taken from non-turret autoattacks by 10%. 850 gold.
• Randuin's Omen: +75 armor, +350 health, +25 health regeneration. Unique Passive: +5% cooldown reduction. Unique Passive: On being hit, 20% chance for attacker's attack speed and movement to be slowed by 35% for 3 seconds. Unique Active: Surrounding units' attack speed and movement are slowed by 35% for 2 seconds plus 0.5 seconds for each 100 armor and magic resistance you have. 60 second cooldown. 3075 gold.
• Sunfire Cape: +45 armor, +450 health. Unique Passive: Nearby enemies suffer 40 magic damage per second. 2610 gold.
• Thornmail: +100 armor. Unique Passive: On being hit, attacker suffers magic damage equal to 30% of the attack's damage (before armor reduction). 2000 gold.
• Warden's Mail: +50 armor, +20 health regeneration. Passive: On being hit, 20% chance for attacker's attack speed and movement to be slowed by 35% for 3 seconds. 1350 gold.
• Wriggle's Lantern: +30 armor, +23 attack damage, +15% life steal. Unique Passive: On hit, 20% chance for target minion/monster to suffer 425 magic damage. Unique Active: Places a Sight Ward at target location. 3 minute cooldown. 1600 gold.
• Zhonya's Hourglass: +50 armor, +100 ability power. Unique Active: For 2 seconds, you are invulnerable and untargetable but cannot take any actions. 90 second cooldown. 3100 gold

Champion abilities

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

• Akali's  Twilight Shroud lays down a cloud of smoke for 8 seconds. While inside of the cloud, she gains 10 / 20 / 30 / 40 / 50 armor.
• Anivia's  Rebirth allows her to enter an egg-state for up to 6 seconds upon reaching 0 health. While in this state, she will receive an armor modifier of −40 / −25 / −10 / +5 / +20.
• Annie's  Molten Shield increases her armor by 20 / 30 / 40 / 50 / 60 for 8 seconds.
• Galio's  Bulwark increases an allied champion's armor by 30 / 45 / 60 / 75 / 90 for 4 seconds.
• Garen's  Courage allows him to increase his armor by 0.5 permanently (max. 25) each time he kills a unit.
• Graves's  True Grit increases his armor by 1 / 2 / 3 every second he remains in combat. This bonus stacks up to 10 times. Graves is considered in combat if he has dealt or received damage in the last 3 seconds.
• Jarvan IV's  Demacian Standard passively increases his armor by 10 / 13 / 16 / 19 / 22. When activated it throws a flag to a target location that grants the passive benefit to nearby allies and to himself again.
• Jax's  Grandmaster's Might increases his armor by 25 / 35 / 45 (+0.3 per bonus attack damage) for 8 seconds.
• Jayce's  Transform: Mercury Hammer increases his armor by 5 / 15 / 25 / 35
• Kennen's  Lightning Rush increases his armor by 10 / 20 / 30 / 40 / 50 for 4 seconds.
• Lee Sin's  Iron Will increases his armor by 10 / 15 / 20 / 25 / 30 for 5 seconds.
• Leona's  Eclipse increases her armor by 30 / 40 / 50 / 60 / 70 for 3 seconds, deals damage after that time to units around her, and retains the defensive buff for an additional 3 seconds if any enemy is struck by the blast.
• Malphite's  Brutal Strikes increases his armor by 20 / 25 / 30 / 35 / 40 % for 6 seconds.
• Master Yi's  Meditate causes him to channel for up to 5 seconds. While channeling his armor is increased by 100 / 150 / 200 / 250 / 300.
• Mordekaiser's  Creeping Death increases an allied unit's armor by 10 / 15 / 20 / 25 / 30 for 6 seconds.
• Nidalee's  Aspect of the Cougar increases her armor by 10 / 20 / 30 while active.
• Olaf's  Ragnarok increases his armor by 30 / 45 / 60 for 6 seconds.
• Orianna's  Command: Protect increases an allied champion's armor by 10 / 15 / 20 / 25 / 30 for as long as the ball is attached to them.
• Poppy's  Paragon of Demacia increases her armor by 1.5 / 2 / 2.5 / 3 / 3.5 for 5 seconds upon attacking or being hit by an enemy (stacks up to 10 times). She can also activate this ability to gain max stacks.
• Rammus's  Defensive Ball Curl increases his armor by 40 / 60 / 80 / 100 / 120 for 6 seconds.
• Shyvana's  Dragon's Descent passively increases her armor by 10 / 15 / 20. This bonus is doubled while she is in Dragon Form.
• Singed's  Insanity Potion increases his armor by 35 / 50 / 65 for 25 seconds.
• Sona's  Aria of Perseverance:
  • Aura: increases nearby allied champions' armor by 3 / 6 / 9 / 12 / 15 while active and persists for two seconds after deactivation.
  • Activation: increases hers and one nearby allied champion's armor by an extra 8 / 11 / 14 / 17 / 20 for 3 seconds.
• Soraka's  Astral Blessing increases an allied unit's armor by 25 / 45 / 65 / 85 / 105 for 5 seconds.
• Taric's  Shatter passively increases his armor by 10 / 15 / 20 / 25 / 30 while the ability is not on cooldown and grants himself and nearby allied units' the same bonus again as a permanent aura.
• Trundle's  Agony targets an enemy to steal their armor by 15 / 20 / 25 %. This amount is doubled over the next 6 seconds. Trundle increases his own armor by the same flat amount as the armor they enemey lost.
• Urgot's  Hyper-Kinetic Position Reverser increases his armor by 60 / 90 / 120 for 5 seconds upon activation.
• Wukong's  Stone Skin passively grants him 4 / 6 / 8 armor for each nearby enemy champion.
• Xerath's  Ascended Form passively grants 15% of his ability power as bonus armor.
• Xin Zhao's  Crescent Sweep increases his armor by 25 (+7/10/13 for each enemy champion hit) for 8 seconds.

Masteries

• Hardiness increases your champion's armor by 2 / 4 / 6.

Runes

• Defense and Resilience runes also increase armor.

Ways to reduce armor

See armor penetration. Note that armor penetration and armor reduction are different.

List of champions' armor

The Highest and Lowest Armor Champions (Base Armor)

Champion Level	Top 5 Champions		Bottom 5 Champions
Level 1	1. 20px Darius	(23.5 armor)	1. Heimerdinger	(10 armor)
	2. Skarner	(22.8 armor)	2. Zilean	(10.55 armor)
	3. Cho'Gath	(22.5 armor)	3. Orianna	(11 armor)
	4. Maokai	(22 armor)	4. Soraka	(11.2 armor)
	4. Poppy
	5. Malphite	(21.75 armor)	5. Sona	(11.3 armor)
Level 18	1. Maokai	(90 armor)	1. Heimerdinger	(61 armor)
	1. Poppy
	3. Hecarim	(88 armor)	2. Orianna	(62 armor)
	4. Skarner	(87.4 armor)	3. Sona	(67.4 armor)
	5. Pantheon	(87.3 armor)	4. Garen	(67.6 armor)
			4. Trundle
	Notes: Taric's  Shatter and Shyvana's  Dragon's Descent passively increase their respective armor to 104 and 99 at level 18, topping the charts. In addition, Jarvan IV's  Demacian Standard passively increases his armor to 90 at level 18, tying with Maokai and Poppy.

Trivia

A level 18 Malphite with 6 Thornmails, 3 points in Hardiness,  Astral Blessing,  Bulwark,  Aria of Perseverance,  Command: Protect, Aegis of the Legion aura, Marks and Glyphs of Resilience, Seals and Quintessences of Defense, and  Brutal Strikes enabled will give a total of approximately 1461 armor. Switching Orianna for Trundle and having an enemy Trundle with the same setup use  Agony on Malphite and the allied Trundle use  Agony on the enemy Trundle, will yield a total of approximately 1864 armor. This is the highest possible amount of armor, which is 94.9% reduction.