Making an Attack Roll
Roll a d20 and add your attack bonus (ability modifier + proficiency bonus if you're proficient with the weapon or spell). If the total equals or exceeds the target's Armor Class (AC), you hit. A natural 20 always hits; a natural 1 always misses.
Critical Hits
Rolling a natural 20 is a critical hit: roll all the attack's damage dice twice and add them together, then add modifiers once. (Some features expand crit range, e.g. crits on 19–20.)
Cover
- Half cover (+2 AC)
- An obstacle blocks at least half the target — another creature, furniture, a low wall.
- Three-quarters cover (+5 AC)
- The obstacle blocks about three-quarters of the target — an arrow slit, a portcullis.
- Total cover
- The target can't be targeted directly by an attack or spell, though some area effects still reach.
Unseen Attackers and Targets
If you can't see the target (darkness, invisibility, blindness), you attack with disadvantage. If the target can't see you, you attack with advantage. If both are true, they cancel out. When attacking a target you can't see, you must guess its location — guess wrong and you miss automatically.
Melee vs. Ranged
Melee attacks have disadvantage against a prone target only if you're more than 5 feet away — within 5 feet you have advantage. Ranged attacks have disadvantage against a prone target, and against any target within 5 feet of a hostile creature that can see you and isn't incapacitated.