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Armour

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Armour is a form of defence that reduces incoming physical damage from hits. Along with Evasion and Energy shield, Armour is one of the three defence types that can implicitly appear on equipment. Unlike resistance, Armour reduces damage by up to a constant value, rather than a proportion of the total damage: every 10 points of Armour blocks up to 1 physical damage per hit. The absolute amount of damage reduced gets closer to the maximum the more damage the hit does.

Armour rating can be increased by wearing equipment, taking certain passive skills, using spells such as Molten Shell, and drinking a Granite FlaskGranite FlaskLasts 4 Seconds
Consumes 30 of 60 Charges on use
+3000 to Armour
Requires Level 27Right click to drink. Can only hold charges while in belt. Refills as you kill monsters.
.

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

Mechanics

Damage reduction from armour only reduces physical damage taken from hits. Elemental damage and damage-over-time are not affected.

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 damage reduction is a function of armour rating and the damage taken. Damage reduction is capped at 90%.

Relative Damage Reduction (Base Formula)

This is the base formula all other formulas are based upon. It is used to calculate the damage reduction factor, i.e. the percentage by which the damage is reduced.

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


Required Armor

To calculate the armor you need to mitigate a given amount of damage at specific ratio, you can use this formula:

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


Reverse Damage

You can also calculate the raw damage that would have resulted for a given damage reduction and armour value:

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


Resulting Damage

To calculate the net 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 Damage Reduction

Another way of looking at it is in terms of absolute 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

For example, if you have 1200 armour rating this chart indicates how much damage will be reduced by:

Damage reduction chart.png

The vertical axis is damage reduction percent. The bottom axis is original damage.


Armor v Defense.png

Therefore we can 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.

Skills

The Determination aura increases armour of the character and nearby allies. The Molten Shell and Vaal Molten Shell skills temporarily grants player additional armour.

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
    • 12% increased Armour
    • 14% increased Armour
    • 15% increased Armour
Armour and Energy Shield
  • 8% increased Armour
  • 5% increased maximum Energy Shield
Armour and Evasion
  • 12% increased Evasion Rating and Armour
Armour and Life Regeneration
  • 10% increased Armour
  • 0.3% of Life Regenerated per Second
Life and Armour
    • 6% increased Armour
    • 5% increased maximum Life
    • 6% increased Armour
    • 4% 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
Sword Damage and Armour
  • 10% increased Physical Damage with Swords
  • 8% 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
Sanctity
  • 20% increased Armour
  • 10% increased maximum Energy Shield
  • 1% of Life Regenerated per Second
  • +10 Strength and Intelligence
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
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
Soul of Steel
  • 30% increased Armour
  • +4% to all Elemental Resistances
  • 4% additional Physical Damage Reduction
Sentinel
  • 24% increased Evasion Rating and Armour
  • +10% to all Elemental Resistances
Steel Skin
  • 30% increased Armour
Iron Reflexes
  • Converts all Evasion Rating to Armour
  • Dexterity provides no bonus to Evasion Rating

Armour rating on shields

These passive skills grant increased armour rating from equipped shields.

Name Bonuses
Shield Armour
  • 30% increased Armour from equipped Shield
Plated Defences
  • 4% additional Chance to Block with Shields
  • 50% increased Armour from equipped Shield

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 Block chance

References

  1. VictorDoom (May 10, 2013). "Unique Items List - 159 of 159". Official Path of Exile Forums. Retrieved June 27, 2013.