Attack Roll

An attack roll represents your attempt to strike your opponent. Your attack roll is 1d20 + your attack bonus with the type of attack you’re using. If the result equals or exceeds the target’s AC, you hit and deal damage.

AUTOMATIC MISSES AND HITS

A natural 1—when the d20 comes up 1—on the attack roll is always a miss. A natural 20—when the d20 comes up 20—is always a hit. A natural 20 is also a threat, which is a possible critical hit.

++Attack Roll Modifiers

Attacker is …	Melee	Ranged
Attacking an off-balance swimmer	+2	+2
Dazzled	-1	-1
Dealing lethal damage with a nonlethal weapon	-4	-4
Dealing nonlethal damage with a lethal weapon	-4	-4
Energy drained1	-1	-1
Entangled2	-2	-2
Fighting defensively	-4	-4
Flanking defender	+2	-
Grappling and attacking with an unarmed strike, natural weapon, or light weapon	-4	-
Grappling and attacking with an opponent's weapon after a successful grapple check	-4	-
Invisible3	+2	+2
Loser in a duel of wills (intimidate)	-1	-1
Nonproficient with armor worn5	Varies	Varies
Nonproficient with weapon used	-4	-4
On higher ground than defender	+1	-
Prone6	-4	-
Shaken or frightened	-2	-2
Shooting or throwing from range7	-	-2
Shooting into melee	-	-4
Squeezing	-4	-4
Subject to rain, severe wind, sleet, or snow	-	-4
Underwater8	Varies	Varies
Using an improvised weapon	-4	-4
Using an inappropriately sized weapon9	-2	-2
Winner in a duel of wills (Intimidate)10	+1	+1

1. Cumulative per negative level.
2. Attacker takes a -4 penalty to Dexterity, which might affect the attack roll.
3. Bonus doesn't apply if defender is blinded.
4. Penalty is only on rolls against the winner. If defender submitted, the penalty lasts for 1 round. If defender participated, the penalty also applies on damage rolls and lasts for the entire encounter.
5. Armor check penalty applies on attack rolls.
6. Most ranged weapons can't be used while the attacker is prone, but you can use a crossbow or shuriken while prone at no penalty.
7. Cumulative per range increment from defender.
8. See Underwater Combat
9. Cumulative per size category of difference.
10. Bonus is only on rolls against defender that ignored or participated in the duel. If defender ignored you, and you succeeded on a DC 15 Intimidate check, the bonus is a morale bonus that lasts for 1 round. If defender participated and lost, the bonus is untyped and also applies on damage rolls, and it lasts for the encounter.