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Armor is a statistic that reduces incoming physical damage. All units have the armor stat. Champions have base armor that, by default, increases through growth by level.

Armor can be gained by abilities, items, and runes. It .

At level 18, base armor ranges from 28 () whose base armor does not scale with levels or 66.6 () to 129 ().

Formula

The formula to calculate post-mitigation physical damage based on raw physical damage received:

Due to the order of operations for penetration and reductions of either resistance, negative values almost never occur. For all non-negative resistance values this means using:

Solving the above formula for raw damage r gives

To determine how much damage will be dealt using raw and a given armor value we can use this formula:

Post Mitigation Damage  =  Raw Damage  ÷  (1  +  (Armor  ÷  100))

Examples using 1,000 raw damage

• 25 armor → 1,000  ÷  (1  +  25  ÷  100)  =  1,000  ÷  1.25  =  800
• Total damage reduction 20%,  + 25% effective health, 1,000 post-mitigation damage  =  1,250 Raw Damage
• 100 armor → 1,000  ÷  (1  +  100  ÷  100)  =  1,000  ÷  2  =  500
• Total damage reduction 50%,  + 100% effective health, 1,000 post-mitigation damage  =  2,000 Raw Damage
• 200 armor → 1,000  ÷  (1  +  200  ÷  100)  =  1,000  ÷  3  =  333.34
• Total damage reduction 66.66%,  + 200% effective health, 1,000 post-mitigation damage  =  3,000 Raw Damage

Gold Value ​​​​

• Armor has a gold value of 20 per point.

Negating Armor

Armor can be negated by armor penetration, armor reduction, and Lethality. The damage calculation then uses the effective armor values after the reduction; the actual damage formulae are not changed.

Armor penetration, Lethality and armor reduction can be treated as negative armor in damage calculations.

Stacking Armor

Following the above damage formula, each point of armor increases the effective health pool against physical damage by 1%, formally:

Example: A unit with 60 armor has 60% increased health against physical attacks. If the unit had 1000 maximum health it would take 1600 physical damage to kill it.

By definition, armor does not give diminishing returns of effective health. Each additional point of armor increases the effective health pool (against physical damage) by 1% of your maximum health. This is not changed by any amount of armor already held.

This would mean that armor gives constant returns. Armor can, however, give increasing returns if a unit has a source of flat post-mitigation damage reduction such as or .

When a unit's armor is negative due to armor reduction debuffs, armor has increasing returns with respect to itself. This is because negative armor cannot reduce effective health to less than 50% of actual health. A unit with -100 armor has 66.67% of nominal health (gains −33.33%) of its maximum health as effective health.

Armor as scaling

These use the champion's armor to increase the magnitude of the ability. It could involve total or bonus armor. By building armor items, you can receive more benefit and power from these abilities.

Increasing armor

Items

This table is automatically generated based on the data from Module:ItemData/data.

ItemCostAmountAvailability
1400 30All maps
800 30All maps
800 40All maps
300 15All maps
2900 45All maps
3300 45All maps
2500 40All maps
2500 30All maps
3200 50All maps
2800 25All maps
2500 80All maps
3200 60All maps
900 20All maps
2800 40Summoner's Rift, Nexus Blitz
2500 30All maps
1100 20All maps
2700 80All maps
2500 40All maps
2800 40All maps
1000 15All maps
3200 35All maps
2700 60All maps
2800 25All maps
2800 40All maps
1000 40All maps
2400 25All maps
2600 45All maps

Armor vs. Health

Note: The following information similarly applies to magic resistance. As of season six, the base equilibrium line for armor is a function:

health = 7.5 × (armor + 100)

while for magic resistance the line is a bit shifted down and less steep:

health = 6.75 × (magic resistance + 100)

It can be helpful to understand the equilibrium between maximum health and armor, which is represented in the graph[1] on the right. The equilibrium line represents the point at which your champion will have the highest effective health against that damage type, while the smaller lines represent the baseline progression for each kind of champion from level 1-18 without items. You can also see that for a somewhat brief period in the early game health is the most gold efficient purchase, however this assumes the enemy team will only have one type of damage. The more equal the distribution of physical damage/magic damage in the enemy team, the more effective will buying health be.

There are many other factors which can effect whether you should buy more armor or health, such as these key examples:

• Unlike HP, increasing armor also makes healing more effective because it takes more effort to remove the unit's HP than it does to restore it.
• HP helps you survive both magic damage and physical damage. Against a team with mainly burst or just low magic damage, HP can be more efficient than MR.
• Percentage armor reduction in the enemy team tilts the optimal health:armor ratio slightly in the favor of HP.
• Whether or not the enemy is capable of delivering true damage or percent health damage, thus reducing the value of armor and health stacking respectively.
• The presence of resist or HP steroids built into your champion's kit, such as in or .
• Against sustained damage life steal and healing abilities can be considered as contributing to your maximum HP (while being mostly irrelevant against burst damage).
• The need to prioritize specific items mainly for their other qualities (regardless of whether or not they contribute towards the ideal balance between HP and resists).

List of champions' armor

Champions with the lowest or highest armor before items, runes, or abilities
Champion Level Top 5 champions Bottom 5 champions
Level 1 1.
1.
47 armor 1. 17 armor
2. 45 armor 2.
2.
2.
2.
2.
18 armor
3. 44 armor 3.
3.
3.
3.
3.
3.
3.
19 armor
4. 42 armor 4. 20 armor
5.
5.
5.
40 armor 5.
5.
5.
5.
5.
21 armor
Level 18 1. 129 armor 1. 28 armor
2. 115 armor 2. 66.6 armor
3. 109.1 armor 3. 68 armor
4. 108.25 armor 4.
4.
4.
70 armor
5. 108.2 armor 5. 71 armor

Optimal efficiency (theoretical)

Note: Effective burst health, commonly referred to just as 'effective health', describes the amount of raw burst damage a champion can receive before dying in such a short time span that he remains unaffected by any form of health restoration*. Unless champion's resists aren't reduced below zero, it will always be more than or equal to a champion's displayed health in their health bar and can be increased by buying items with extra health, armor and magic resistance. In this section, effective health will refer to the amount of raw 'physical damage' a champion can take.

In almost all circumstances, champions will have more maximum health than armor, thus a single point of armor will give more 'effective health' to a champion than a single point of health. However, if there is a case where max health is below the value of 'armor + 100', the opposite becomes true.

Because of this relationship, theoretically, maximum effective health is attained by ensure that you have exactly 100 more max health than armor, regardless of how much health or armor you actually already have.

Example: Given a theoretical situation where you start off with 1 health and 1 armor and are given an arbitrary sufficient number of stat points (x ≥ 100), each of which you can use to increase either your health or armor by 1 point, the way to maximize your effective health is to add points to your health until your health has 100 more points than armor, then split the remaining stat points in half and share them between your health and armor.

However, this is only theoretically true if we consider both health and armor to be equally obtainable resources with simplified mechanism of skill point investment. In reality a player buys these stats for gold instead. So when attempting to ensure the balance of 'health = armor + 100', consider it through gold value distributed to the stats. Because the gold value of 1 health is roughly 7.7 times smaller than 1 point of armor (as of V8.7), distribution per point of health or armor should be 11.5% gold into health and 88.5% gold into armor once the 'health = armor + 100' equilibrium is reached.

This model is highly simplified and cannot be exactly applied when buying any other item that aren't purely armor or health oriented as they deviate the equilibrium. Going even further, the continuous model simplifies a discrete character of real shopping, as you cannot really buy 1.5 ×  for 600, so you either opt to buy a single or 2 × , drastically unbalancing the equilibrium.

Broadly speaking, items which provide both health and armor give a very high amount of effective health against physical damage compared to items which only provide health or only provide armor. These items should be purchased when a player is seeking efficient ways to reduce the physical damage they take by a large amount. Furthermore, these items are among all available items the best ones to distribute their gold value equally among both health and armor, thus working perfectly for rule of preserving equilibrium.

Conclusion

This information is strongly theoretical. Due to how there are many variables aside from health, armor and gold value, "true equilibrium" is too complicated and unrealistic to achieve. However, a player can develop their intuition to itemize towards this equilibrium in a timely manner through the experience gained from the multitude of plays they perform.

The important thing to remember is that there is no reason to hold to the equilibrium too strictly, or else you might just lose the fun out of the game.

Trivia

• The old stat icon for armor seems to based on the old icon of .

Last updated: July 29, 2020, patch V10.15

Without using , or with which potentially allow for infinite amounts of armor, the largest amount of armor is reached with a level 18 at 3104 armor (which reduces physical damage by 96.88%).

• Runes:
• Items:
• 5 ×
• 1 ×
• Buffs:
• has a to shield to whole team, triggering .
• 4 ×
• :
• Base armor = 97.8 armor
• Items = + = 675 armor
• Runes = + + + 6 × 2 = 181 armor
• Armor Multiplier = 1 + + = 1.29
• armor = (97.8 + 675 + 181) × 1.29 = 1230.402 armor
• bonus = 1230.402 × 0.14 = 172.25628 bonus armor
• :
• Items = + = 675 armor
• Runes = + + + 6 × 2 = 181 armor
• Armor Multiplier = 1 + + = 1.29
• armor = (675 + 181) × 1.29 = 1104.24 bonus armor
• bonus = 26 + 1104.24 × 0.12 = 158.5088 bonus armor
• :
• Base armor = 109.1 armor
• Items = + = 675 armor
• Runes = + + + 6 × 2 = 181 armor
• Buffs = + + + = 390.76508 armor
• Armor Multiplier = 1 + + + = 2.29
• armor = (109.1 + 675 + 181 + 390.76508) × 2.29 = 3104.9310332 armor

, with his effectively infinite stacking, can obtain a maximum of 749999.25 armor off his passive alone. With the same set-up as above, he can obtain a total of about 910296.7564 armor, reducing physical damage by 99.99989016%.