How Cover Works in 5e (and the Rulings That Start Arguments)

Cover is easy to read and easy to get wrong. The rules take up half a page, but I keep seeing the same fights break out at the table. Does a low wall actually help. Does it stack. Does hiding behind the fighter do anything. Almost all of it comes down to two or three lines the book states plainly and most people forget. Here’s how I run it, and why.

The three tiers

There are three grades of cover, and a target only ever gets one of them at a time: the best one that applies.

Cover	AC bonus	Dex save bonus	Where it comes from
Half	+2	+2	A low wall, a barrel, another creature
Three-quarters	+5	+5	An arrow slit, a thick trunk, a portcullis
Total	Can’t be targeted	n/a	A solid wall, a closed door, a stone pillar

Total cover is the one people misread. “Can’t be targeted directly” doesn’t mean safe. It means a single attack, or a spell that needs a creature you can see, has no line to them. Drop a fireball next to the pillar and they still cook.

How you actually check it

Cover comes from something between the attacker and the target that blocks part of the line to them. The book is specific about how you measure:

Choose a corner of the attacker’s space. Trace imaginary lines from that corner to every corner of one square the target occupies. If one or two of those lines are blocked, the target has half cover. If three or four are blocked but the attack can still reach, it’s three-quarters cover.

The part that gets skipped: you measure from a single corner of the attacker’s space, and the attacker picks it. So the shooter chooses the angle that gives up the least cover. In play, cover is stingier than it looks on the grid.

The calls that cause fights

A few rulings settle most of the disputes.

Cover doesn’t stack. Two low walls are not +4. Crouching behind a crate while also peeking around a corner is still half cover, not both. Pick the single best tier and move on.

Creatures only ever give half cover. A Medium ally in the way is +2, and that’s it. Size doesn’t change it. That’s why parking the barbarian in the doorway helps a little but never turns him into a wall.

Cover stops attacks aimed at the target, not blasts centered nearby. This is the flip side of the total-cover rule. A pillar can break the wizard’s line of sight to your rogue and still do nothing about the lightning bolt coming down the corridor, because the bolt traces its own line from its own origin.

A quick example

This is the one that came up at my table a couple weeks ago.

Archer (A) shoots a goblin (G) crouched behind a 3-ft crate.

  . . . . .
  . A . . .
  . . # . .     # = crate
  . . G . .
  . . . . .

Trace from a corner of A to the four corners of G:
  2 of the 4 lines clip the crate  ->  half cover
  Goblin AC 15 plays as AC 17 against this shot

Because the archer picks the corner, moving one square before the shot can drop the goblin’s cover entirely. That turns positioning into a real decision instead of set dressing, which is most of what I want out of a combat rule.

What I tell new GMs

Run it this way and the low-wall argument mostly stops happening:

1. Use the best single tier. Never add them up.
2. Trace from one corner of the attacker’s space, and let the attacker choose it.
3. Creatures give half cover and nothing more.
4. Total cover stops attacks aimed at the target, not blasts centered nearby.
5. The bonus covers AC and Dexterity saves, so remember it when the save-for-half spells start flying down the hall.

None of this adds bookkeeping. It just makes the battlefield matter, which is the whole reason you put walls on the map in the first place.