Armour

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Armour is a form of defence that mitigates incoming physical damage from hits when all avoidance forms have failed.

Along with evasion and energy shield, armour is one of the three defence types that can implicitly appear on equipment. Unlike resistance, armour has diminishing returns as it's effectiveness is based on the magnitude of incoming physical damage (multiplied by 10). As a result armour is most effective in mitigating small hits (i.e. 50% and better reduction for initial damage less then a tenth of the armor value) and least effective in mitigating very large hits (where it's absolute reduction can at most be one tenth of the armor value).

Armour rating can be increased by wearing equipment, taking certain passive skills, using spells such as Molten Shell inventory icon.pngMolten Shell
Molten ShellSpell, AoE, Duration, Fire
Radius: 15
Mana Cost: (8 to 28)
Cast Time: 0.50 sec
Critical Strike Chance: 5.00%
Damage Effectiveness: 200%
Drop Level: 4
Requires Level 4
Summons fiery elemental shields providing additional armour for a short duration. If cumulative physical damage prevented by your blocking or armour reaches a threshold, the shields explode outwards, dealing fire damage to surrounding enemies.Per 1% Quality:
1% chance to Ignite enemies
Deals (14 to 1962)-(20 to 2943) Fire Damage
Shields break after (26 to 1508) total Damage is prevented
(17 to 943) additional Armour
Base duration is 10.0 seconds
Place into an item socket of the right colour to gain this skill. Right click to remove from a socket.
Molten Shell inventory icon.pngMolten Shell skill icon.png
, and drinking a Granite FlaskGranite FlaskLasts 4 Seconds
Consumes 30 of 60 Charges on use
+3000 to Armour
Requires Level 27
Right click to drink. Can only hold charges while in belt. Refills as you kill monsters.
.

Basalt FlaskBasalt FlaskLasts 5.00 Seconds
Consumes 40 of 60 Charges on use
20% additional Physical Damage Reduction
20% of Melee Physical Damage taken reflected to Attacker
Requires Level 40
Right click to drink. Can only hold charges while in belt. Refills as you kill monsters.
grants additional physical damage reduction.

Supposedly the most armour monsters have in the game is about 983.[1]

Mechanics

Physical damage reduction from armour only mitigates physical damage from hits. It falls under the modifier #% additional Physical Damage Reduction when Hit. Physical Damage Reduction is capped at 90%. [2]

Elemental damage and damage over time are not mitigated by armour, because armour only mitigates physical damage from hits. Bleed is a damage over time debuff that is based on the initial physical hit, armour would reduce the initial hit but not the damage over time. However both the initial hit and the damage over time can be mitigated with other sources for example Basalt FlaskBasalt FlaskLasts 5.00 Seconds
Consumes 40 of 60 Charges on use
20% additional Physical Damage Reduction
20% of Melee Physical Damage taken reflected to Attacker
Requires Level 40
Right click to drink. Can only hold charges while in belt. Refills as you kill monsters.
or endurance charges because they don't only apply to hits.

rule of thumb

  • To prevent one third of damage, you need armor 5 times the damage (e.g. 500 Armor for 100 damage)
  • To prevent half of damage, you need armor 10 times the damage (e.g. 1000 Armor for 100 damage)
  • To prevent two thirds of damage, you need armor 20 times the damage (e.g. 2000 Armor for 100 damage)
  • To prevent three quarters of damage, you need armor 30 times the damage (e.g. 3000 Armor for 100 damage)
  • To prevent 90% of damage, you need armor 90 times the damage (e.g. 9000 Armor for 100 damage)

Formulas

The amount of physical damage reduction is a function of armour rating and the physical damage taken.

Relative Physical Damage Reduction (Base Formula)

This is the base formula all other formulas are based upon. It is used to calculate the #% additional Physical Damage Reduction when Hit factor, i.e. the percentage by which the physical damage is mitigated.

DR(A, D_{raw}) = {A \over A + 10 * D_{raw}}

where A is the defender's armour rating and Draw is the raw physical damage.

Required Armour Rating

To calculate the armour rating you need to mitigate a given amount of Physical Damage at specific ratio, you can use this formula:

A(D_{raw}, DR) = {DR * 10 * D_{raw} \over 1 - DR}


Reverse Physical Damage

You can also calculate the raw physical damage that would have resulted for a given Physical Damage Reduction and Armour rating:

D_{raw}(A, DR) = {A \over 10 * DR} - {A \over 10}


Resulting Physical Damage

To calculate the net physical damage (i.e. the damage after damage reduction, the following formula can be used:

D_{net}(A, D_{raw}) = {10 * {D_{raw}}^2 \over A + 10 * D_{raw}}


Absolute Physical Damage Reduction

Another way of looking at it is in terms of absolute physical damage reduction:

DR_{abs}(A, D_{raw}) = {A * D_{raw} \over A + 10 * D_{raw}}


Defense factor

DF(A, D_{raw}) = {A \over 10 * D_{raw}} + 1

examples

The plot below displays how much damage reduction occurs at different armour ratings and raw physical damage.

Armour reduction at varying armour ratings and raw physical damage


From the plot below we can further conclude:

  • If raw damage is much less than Armour / 10, raw damage has a near-quadratic effect on net damage. Equivalently, in this regime raw damage has a near-linear effect on net DPS if the raw DPS is held constant.
  • If raw damage is much greater than Armour / 10, raw damage has a near-linear effect on net damage. Equivalently, in this regime raw damage has little effect on net DPS if the raw DPS is held constant.
  • Against attacks of a fixed raw damage, armour has a linear effect on the number of attacks it takes to deplete a certain amount of hit points.

Armor v Defense.png

Skills

The Determination inventory icon.pngDetermination
DeterminationAura, Spell, AoE
Radius: 36
Mana Reserved: 50%
Can store 1 use(s)
Cooldown Time: 1.20 sec
Cast Time: 1.20 sec
Drop Level: 24
Requires Level 24
Casts an aura that grants armour to you and your allies.Per 1% Quality:
1% increased Area of Effect radius
You and nearby allies gain (32 to 51)% more Armour
(0 to 40)% increased Area of Effect radius
Place into an item socket of the right colour to gain this skill. Right click to remove from a socket.
Determination inventory icon.pngDetermination skill icon.png
aura increases armour of the character and nearby allies. The Molten Shell inventory icon.pngMolten Shell
Molten ShellSpell, AoE, Duration, Fire
Radius: 15
Mana Cost: (8 to 28)
Cast Time: 0.50 sec
Critical Strike Chance: 5.00%
Damage Effectiveness: 200%
Drop Level: 4
Requires Level 4
Summons fiery elemental shields providing additional armour for a short duration. If cumulative physical damage prevented by your blocking or armour reaches a threshold, the shields explode outwards, dealing fire damage to surrounding enemies.Per 1% Quality:
1% chance to Ignite enemies
Deals (14 to 1962)-(20 to 2943) Fire Damage
Shields break after (26 to 1508) total Damage is prevented
(17 to 943) additional Armour
Base duration is 10.0 seconds
Place into an item socket of the right colour to gain this skill. Right click to remove from a socket.
Molten Shell inventory icon.pngMolten Shell skill icon.png
and Vaal Molten Shell inventory icon.pngVaal Molten Shell
Vaal Molten ShellVaal, Spell, AoE, Duration, Fire
Souls per use: 48 (N) / 72 (C) / 96 (M)
Can store 1 use(s)
Cast Time: 0.50 sec
Critical Strike Chance: 5.00%
Damage Effectiveness: 200%
Drop Level: 4
Requires Level 4
Summons fiery elemental shields providing additional armour for a short duration. For each hit you take, the shields cause a burst of flame, dealing fire damage to surrounding enemies.Per 1% Quality:
1% chance to Ignite enemies
Deals (9 to 1373)-(14 to 2060) Fire Damage
(17 to 943) additional Armour
Base duration is 10.0 seconds
Corrupted
Place into an item socket of the right colour to gain this skill. Right click to remove from a socket.
Vaal Molten Shell inventory icon.pngVaal Molten Shell skill icon.png
skills temporarily grants player additional armour. The Summon Chaos Golem inventory icon.pngSummon Chaos Golem
Summon Chaos GolemGolem, Chaos, Minion, Spell
Mana Cost: (30 to 54)
Can store 1 use(s)
Cooldown Time: 6.00 sec
Cast Time: 1.00 sec
Drop Level: 34
Requires Level 34
Summons a Chaos Golem that grants you Physical Damage Reduction. The Chaos Golem can use a damage over time Chaos aura and a cascade of Chaos spikes in addition to its melee attack.Per 1% Quality:
1% increased Minion Maximum Life
1% increased Minion Damage
(0 to 10)% increased Character Size
Can raise up to 1 Golem at a time
Golems grant (3 to 4)% additional Physical Damage Reduction
(30 to 68)% increased Minion Maximum Life
Place into an item socket of the right colour to gain this skill. Right click to remove from a socket.
Summon Chaos Golem inventory icon.pngSummon Chaos Golem skill icon.png
increase physical damage reduction, but not armour.

Unique jewels

The following jewels affect Armour:

NameBase ItemLimitRadiusModifiers
Energised Armour
Crimson JewelN/ALarge
(15 to 20)% increased Armour
Increases and Reductions to Energy Shield in Radius
are transformed to apply to Armour at 200% of their value
Survival Skills
Crimson Jewel1N/A
10% increased Physical Damage
+50 to Armour
The Vigil
Crimson JewelN/AMedium
(8 to 15)% increased Armour
With at least 50 Strength Allocated in Radius, Vigilant Strike
also Fortifies Nearby Allies for 3 seconds.

Passive skills

There are passive skills that grant armour bonuses.

Armour rating

These passive skills grant increased armour rating or additional base armour rating. The Iron Reflexes keystone is special in that it converts evasion rating to armour rating.

Name Bonuses
Armour
    • 8% increased Armour
    • 12% increased Armour
    • 14% increased Armour
    • 15% increased Armour
Armour and Energy Shield
    • 8% increased Armour
    • 5% increased maximum Energy Shield
    • 10% increased Armour
    • 5% increased maximum Energy Shield
Armour and Evasion
  • 12% increased Evasion Rating and Armour
  • +3% to all Elemental Resistances
Armour and Life Regeneration
  • 10% increased Armour
  • 0.3% of Life Regenerated per Second
Armour, Evasion and Life
  • 6% increased Evasion Rating and Armour
  • 4% increased maximum Life
Life and Armour
    • 6% increased Armour
    • 4% increased maximum Life
    • 6% increased Armour
    • 5% increased maximum Life
    • 8% increased Armour
    • 4% increased maximum Life
    • 12% increased Armour
    • 4% increased maximum Life
    • 16% increased Armour
    • +16 to maximum Life
Mace Damage and Armour
  • 10% increased Physical Damage with Maces
  • 10% increased Armour
Staff and Mace Attack Speed and Armour
  • 3% increased Attack Speed with Staves
  • 3% increased Attack Speed with Maces
  • 10% increased Armour
Armour Mastery
  • 24% increased Armour
  • 3% increased Movement Speed
  • 0.5% of Life Regenerated per Second
Baptism by Light
  • 20% increased Physical Damage with Maces
  • 10% increased Accuracy Rating
  • 10% increased Armour
  • 10% increased Light Radius
Blunt Instrument
  • 28% increased Physical Damage with Staves
  • 28% increased Physical Damage with Maces
  • 30% increased Armour
Bravery
  • 24% increased Evasion Rating and Armour
  • 8% increased Maximum Life
Cloth and Chain
  • 24% increased Evasion Rating and Armour
  • +12% to all Elemental Resistances
Combat Stamina
  • 20% increased Armour
  • 5% increased maximum Life
  • 1% of Life Regenerated per Second
Faith and Steel
  • 20% increased Armour
  • 10% increased maximum Energy Shield
  • +8% to all Elemental Resistances
Indomitable
  • You take 20% reduced Extra Damage from Critical Strikes
  • 30% increased Armour
Juggernaut
  • 16% increased Armour
  • 6% increased maximum Life
  • 20% increased Life Recovery from Flasks
Leather and Steel
  • 24% increased Evasion Rating and Armour
  • Ignore all Movement Penalties from Armour
Path of the Warrior
  • 12% increased Physical Damage
  • +10 to Armour
  • +20 to Strength
Sanctity
  • 20% increased Armour
  • 10% increased maximum Energy Shield
  • 1% of Life Regenerated per Second
  • +10 Strength and Intelligence
Sentinel
  • 24% increased Evasion Rating and Armour
  • +10% to all Elemental Resistances
Soul of Steel
  • 30% increased Armour
  • +4% to all Elemental Resistances
  • 4% additional Physical Damage Reduction
Iron Reflexes
  • Converts all Evasion Rating to Armour
  • Dexterity provides no bonus to Evasion Rating

Armour rating while Fortify

These passive skills grant increased armour rating while you have Fortify.

Name Bonuses
Rampart
  • 20% increased Armour while you have Fortify
  • 10% increased effect of Fortify on you
  • 15% increased Physical Melee Damage while you have Fortify

Miscellany

These passive skills are related to armour, but do not fit into any other category.

Name Bonuses
Acrobatics
  • 30% Chance to Dodge Attacks
  • 50% less Armour and Energy Shield
  • 30% less Chance to Block Spells and Attacks

References

  1. VictorDoom (May 10, 2013). "Unique Items List - 159 of 159". Official Path of Exile Forums. Retrieved June 27, 2013.
  2. Malice (November 14, 2011). "Mechanics Thread". Official Path of Exile Forums. Retrieved November 16, 2015.