Area of effect

Area of effect (often referred to as AoE) refers to an area with radius in where all enemies can be affected by the effect. Skill gems with an area of effect have the AoE gem tag.

Mechanics
The simplest examples are skills like, and , which have circular areas of effect. Skills like and  have cone-shaped effects - effectively cut out of circles. Some skills have irregular shapes, for example or.

Skills that damage multiple enemies per cast do not necessarily have an area of effect. Piercing projectiles like do not have the AoE tag, nor do chaining skills.

Modifiers that increase or decrease area of effect target the total area of the effect. When modifying the area, all applicable skills will be affected, including skills that do not deal damage such as auras. Almost every passive skill, support gem, and item that modifies area of effect modifies the total area, not the radius directly. Since the total area is being increased rather than the radius, the radius is effectively increased by the square root of the increase of area of effect for circular AoE abilities. For example, applying +100% area of effect to an ability with a radius of 10 would increase the radius to 14.1. For abilities with shapes other than a circle, the area is increased as usual for that shape. For example, an ability that hits in a 120° cone would gain 3 times as much increase to radius from area of effect bonuses, due to only hitting a third of a circle.

Some skills gain an increase to the radius of the area of effect as they are leveled. Modifiers that are percentage increases to area of effect (ex. the quality bonus on Contagion, granting +0% to +10% increase area of effect) are additive with other percentage radius modifiers. Modifiers that annotate a specific (usually integer) increase to the radius (ex. the gem level bonus for Caustic Arrow, granting +0 to +6 increased radius) are additive with the base radius, and apply before area of effect modifiers, making them substantially stronger. These direct bonuses to radius are much rarer than increases to area of effect, however, and nearly always occur only as gem level bonuses on the active skill gems themselves.

For example, Caustic Arrow has a base radius of 13 and gains an additional +6 radius (total 19) by gem level 20. This is a 46% increase to the base radius, equivalent to applying +113% area of effect to a level 1 Caustic Arrow, and is multiplicative with normal area of effect bonuses due to applying directly to the base radius. A level 20 Caustic Arrow with +100% area of effect bonus would have a radius of 26.9, more than double the radius of an unbonused level 1 Caustic Arrow.

When an item or skill increases the area damage, it will only be applicable to the part of the skill that deal damage in an area of effect. For example, with, that damage bonus will go into effect only when the projectile explodes on last target struck and won't work if the projectile pierced, chained, or forked. Many abilities that apply a damage over time effect in an area (ex. Contagion, Bane, Soulrend's DoT effect, proliferated Ignite, etc) do not benefit from area damage, but may still benefit from increases to area of effect. This is not universal, however; for example, Caustic Arrow and Toxic Rain both benefit from increases to area damage despite dealing damage over time (the difference may be that these two do not apply a damaging debuff, instead dealing damage based on a ground effect or world object).

Area of effect does not affect the trigger radius of traps and mines, but it can apply to effects cast by the trap or mine. Only passive skills and effects specifying "Trap Trigger Radius" or "Mine Detonation Radius" will affect them specifically. However, area of effect modifiers will apply to effects cast by the trap or mine. The same goes for totems that use effects that have an area of effect as well.

Auras also benefit from general increases to area of effect, and additionally have access to bonuses that are specifically noted as increasing the area of effect of auras (ex. Leadership passive, Victario's Charity). Nearly all auras also gain increased area of effect from their default quality bonus.

Skill gems
All Aura gems have an AoE:

All Curse gems also have an AoE:

A list of support gems with the gem tag: AoE or quality that increases AoE

Unique items
The following unique items are related to area of effect:

Modifiers
The following modifiers are related to area of effect:

Passive skills
There are passive skills that grant bonuses to skills with an area of effect.

Area of effect
These passive skills grant increased area of effect for skills.

Area of effect for auras
These passive skills grant increased area of effect for auras.

Area of effect for curses
These passive skills grant increased area of effect for curses.

Area of effect damage
These passive skills grant increased damage to area of effect skills.

Cluster Jewel passive skills
The following Cluster Jewel passive skills are related to area of effect:

Keystone passive skills
The following keystone passive skills are related to area of effect:

Ascendancy passive skills
The following Ascendancy passive skills are related to area of effect:

Version history

 * In this update, we are removing the concept of "Increased Radius of Area Skills" and replacing it with "Increased Area of Effect" for all skills, items and passives. The broad impact of this change is that early increases to area of effect will be significant and impactful, while every subsequent point will be less and less noticeable. Previously, each point spent towards increasing the radius of area skills was better than the last, making accumulation of the stat far too desirable.
 * }