Armour

This page is about the defensive stat. For equipment classified as armour, see Armour (equipment).

For the basic passive skill, see Armour (passive skill).

Armour is a form of defence that mitigates incoming physical damage from hits. Armour rating can be increased by wearing equipment, taking certain passive skills, using skills (e.g. ), and drinking flasks (e.g. and ).

Mechanics

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 its effectiveness is based on the magnitude of incoming physical damage (multiplied by 5). As a result, armour is most effective in mitigating small hits (i.e. 50% and better reduction for initial damage less than a fifth of the armour value) and least effective in mitigating very large hits (where its absolute reduction can at most be one fifth of the armour value).

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

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%.

Armour does not mitigate damage over time, as armour will only mitigate 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 endurance charges because they don't only apply to hits.

Armour will only mitigate physical damage hits, not for elemental or chaos damage. If the Transcendence keystone is taken, armour mitigates elemental damage hits, but not physical.

Rule of thumb

• To prevent one third of damage, you need armour 2.5 times the damage (e.g. 250 armour for 100 damage)
• To prevent half of damage, you need armour 5 times the damage (e.g. 500 armour for 100 damage)
• To prevent two thirds of damage, you need armour 10 times the damage (e.g. 1000 armour for 100 damage)
• To prevent three quarters of damage, you need armour 15 times the damage (e.g. 1500 armour for 100 damage)
• To prevent 90% of damage, you need armour 45 times the damage (e.g. 4500 armour for 100 damage)
• armour will never prevent more damage than its value divided by 5 (e.g. 1000 armour will never prevent more than 200 damage)

Formulas

For a step by step calculation of formulas, see Armour/math.

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.

$\color[RGB]{163,141,109} DR(A, D_{raw}) = {A \over A + 5 \times D_{raw} }$

where A is the defender's armour rating and D_raw 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:

$\color[RGB]{163,141,109} A(D_{raw}, DR) = {DR * 5 * D_{raw} \over 1 - DR}$

Reverse Physical Damage

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

$\color[RGB]{163,141,109} D_{raw}(A, DR) = {A \over 5 * DR} - {A \over 5}$

Resulting Physical Damage

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

$\color[RGB]{163,141,109} D_{net}(A, D_{raw}) = {5 * {D_{raw} }^2 \over A + 5 * D_{raw} }$

Absolute Physical Damage Reduction

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

$\color[RGB]{163,141,109} DR_{abs}(A, D_{raw}) = {A * {D_{raw} } \over A + 5 * D_{raw} }$

Defense factor

$\color[RGB]{163,141,109} DF(A, D_{raw}) = {A \over 5 * D_{raw} } + 1$

Examples

The plots 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

Mitigated Damage as a function of Incoming Damage and Armour Rating. Note that Rounding is usually decided in the monster's favor.

% Mitigated Damage as a function of Incoming Damage and Armour Rating

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.

Active skill gems

Main page: List of armour related skill gems

Support skill gems

Main page: List of armour related skill gems

Mechanics Scaled by Armour Rating

The following items provide some bonuses that scale with Armour rating.

Unique items

See also: List of unique armours granting armour

Notable Armour Rating

Unique items that can potentially grant upwards of 1,000 Armour rating.

Global Armour increases

Unique items that grant increased global Armour rating.

Global flat Armour

Unique items that grant a flat bonus to global Armour rating.

Passive skills

There are passive skills that grant armour bonuses.

Base passives

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.

Cluster jewel passives

The following cluster jewel-only passives are related to armour: