DnD Cover Rules in Combat

Cover in Dungeons & Dragons is one of those rules that feels obvious until it isn't — a goblin ducks behind a barrel, an archer fires from a murder hole, and suddenly the table is debating whether a half-wall counts. The cover system in 5th Edition D&D gives Dungeon Masters and players a structured way to adjudicate these moments, with two distinct tiers that apply different mechanical penalties to attack rolls and saving throws. Getting this right matters because it's one of the most frequently triggered combat rules in any encounter that takes place somewhere more interesting than an empty field.

Definition and scope

Cover applies when something physically obstructs the line between an attacker and a target. According to the rules as written in the Player's Handbook (Chapter 9, "Combat"), cover is assessed from the attacker's perspective — specifically, from any corner of the attacker's space to any corner of the target's space. If that imaginary line passes through or touches an obstruction, the target has cover.

There are two named tiers in 5th Edition:

1. Half cover — granted by an obstacle that blocks roughly half of the target's body. This imposes a +2 bonus to AC and Dexterity saving throws for the creature benefiting from it.
2. Three-quarters cover — granted by an obstacle that blocks about three-quarters of the target's body, such as a portcullis, a thick tree trunk, or an arrow slit. This imposes a +5 bonus to AC and Dexterity saving throws.

A third condition, total cover, means the target is completely hidden behind an obstruction and simply cannot be targeted directly by attacks or spells at all.

The bonuses stack with a character's base AC — a fighter in plate armor (AC 18) with half cover sits at AC 20 against the triggering attack. That difference is not cosmetic; at moderate challenge ratings, it can shift hit probability by 10 to 15 percentage points.

How it works

The key dimensions and scopes of DnD include a combat system built on spatial logic, and cover follows that same geometry. The Dungeon Master determines cover by checking whether any single line from a corner of the attacker's space to any corner of the target's space passes through an obstruction. If at least one line passes through, cover may apply. If all four lines are blocked, the creature is in total cover.

Creatures can also grant cover. A Large creature standing between a Medium attacker and a Medium target can be ruled to provide half cover depending on the geometry. This is where the DM's spatial judgment matters most — the rules provide the framework, but a grid with measured distances (using 5-foot squares as the standard unit of measurement) makes these calls far more defensible.

Saving throw interaction is worth a specific note: the AC and Dexterity saving throw bonuses apply only when the source of the saving throw is on the opposite side of the cover from the creature. A fireball cast from the same side of the wall as the target doesn't benefit from the wall, even if the target is crouched beside it.

Common scenarios

A few situations come up repeatedly at almost every table:

• Low walls and crates — The most common half-cover trigger. A creature crouching behind a 3-foot stone wall in a dungeon corridor is the textbook case. The wall clearly blocks roughly half the body.
• Arrow slits — Medieval architecture's most aggressive contribution to cover rules. An arrow slit typically grants three-quarters cover to a creature firing from it, because the slit exposes only a narrow slice of the defender.
• Trees in outdoor encounters — A thick tree trunk (often described as 2 to 3 feet in diameter in module encounter notes) grants three-quarters cover. A thin sapling grants none under strict RAW, though many DMs apply half cover.
• Other creatures — A creature using a Large ally as a meat shield gets DM-adjudicated cover. Many tables apply half cover in this case for consistency.
• Prone targets and elevated attackers — Prone creatures gain no automatic cover benefit against ranged attacks from elevated positions, a geometric reality that surprises newer players.

Decision boundaries

The boundary between half cover and three-quarters cover is the most disputed line in the system, and dnd-frequently-asked-questions reflects how often players raise exactly this issue. The official threshold is a judgment call about what fraction of the body is exposed, which means the DM needs a consistent internal standard.

A practical decision framework:

1. Identify the obstruction — Is it a solid object, a creature, or terrain?
2. Estimate exposed area — If roughly 50% of the target is visible, call it half cover (+2). If only roughly 25% is visible, call it three-quarters (+5). If 0% is visible, total cover — no valid target.
3. Check the source direction — Is the attacker on the opposite side of the obstruction from the target? If not, the cover doesn't apply to that specific attacker even if it would apply to someone else.
4. Apply to the correct roll — Remember the bonus applies to AC against the triggering attack and to Dexterity saving throws caused by sources on the far side of the obstruction. It does not apply to other saving throw types, Constitution saving throws, or Wisdom saves.

The how-it-works section of this site addresses broader mechanical interactions, but within the cover rules specifically, the single biggest source of table disputes is misapplying the bonus to the wrong type of roll — particularly extending it to non-Dexterity saves, which the Player's Handbook does not support. Keeping that boundary clean resolves the majority of cover-related arguments before they start.