Cover

Walls, trees, creatures, and other obstacles can provide cover during combat, making a target more difficult to harm. A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.

There are four degrees of cover. If a target is behind multiple sources of cover, only the most protective degree of cover applies, not added together.

A target with one-quarter cover has a +2 bonus to AC and Dexterity saving throws. A target has one-quarter cover if an obstacle blocks at least one-fourth of its body, such as a thin pillar or a creature of one size category smaller.

A target with half cover has a +3 bonus to AC and Dexterity saving throws. A target has half cover if an obstacle blocks at least half of its body, such as a low wall or a creature of the same size category.

A target with three-quarters cover has a +5 bonus to AC and Dexterity saving throws. A target has three-quarter cover if about three-quarters of it is obstructed, whether by an obstacle or a creature of one size category larger.

A target with total cover can't be targeted directly by an attack or a power, although some powers can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.

Variant: Creatures Providing Cover

Sometimes, creatures in close proximity create a veritable mess of bodies, potentially causing attacks targeting one to hit another. Using this variant, if an attack would miss a creature by an amount less than or equal to the bonus to AC granted by the cover of another creature, and the attack would hit that other creature, the GM might consider having that other creature take the attack's damage.