This section summarizes the statistics that determine success in combat, and then details how to use
An attack roll represents your attempt to strike your opponent on your turn in a round. When you make an attack roll, you roll a d20 and add your attack bonus. (Other modifiers may also apply to this roll.) If your result equals or beats the target’s Armor Class, you hit and deal damage.
Automatic Misses and Hits
A natural 1 (the d20 comes up 1) on an attack roll is always a miss. A natural 20 (the d20 comes up 20) is always a hit. A natural 20 is also a threat—a possible critical hit.
Your attack bonus with a melee weapon is:
Base attack bonus + Strength modifier + size modifier
Your attack bonus with a finesse weapon is:
Base attack bonus + Dexterity modifier + size modifier
With a ranged weapon, your attack bonus is:
Base attack bonus + Dexterity modifier + size modifier + range penalty
Base Attack Bonus
A base attack bonus is an attack roll bonus derived from character class and level or creature type and Hit Dice (or combinations thereof). Base attack bonuses increase at different rates for different character classes and creature types. A second attack is gained when a base attack bonus reaches +6, a third with a base attack bonus of +11 or higher, and a fourth with a base attack bonus of +16 or higher. Base attack bonuses gained from different sources, such as when a character is a multiclass character, stack.
When your attack succeeds, you deal damage. The type of weapon used determines the amount of damage you deal. Effects that modify weapon damage apply to unarmed strikes and the natural physical attack forms of creatures.
Damage reduces a target’s current hit points.
If penalties reduce the damage result to less than 1, a hit still deals 1 point of damage.
When you hit with a melee or thrown weapon, including a sling, add your Strength modifier to the damage result. A Strength penalty, but not a bonus, applies on attacks made with a bow that is not a composite bow.
When you deal damage with a weapon in your off hand, you add only ½ your Strength bonus.
Wielding a Weapon Two-Handed
When you deal damage with a weapon that you are wielding two-handed, you add 1½ times your Strength bonus. However, you don’t get this higher Strength bonus when using a light weapon with two hands.
Sometimes you multiply damage by some factor, such as on a critical hit. Roll the damage (with all modifiers) multiple times and total the results. Note: When you multiply damage more than once, each multiplier works off the original, unmultiplied damage.
Exception: Extra damage dice over and above a weapon’s normal damage are never multiplied.
Certain creatures and magical effects can cause temporary ability damage (a reduction to an ability score).
Your Armor Class (AC) represents how hard it is for opponents to land a solid, damaging blow on you. It’s the attack roll result that an opponent needs to achieve to hit you. Your AC is equal to the following:
Note that armor limits your Dexterity bonus, so if you’re wearing armor, you might not be able to apply your whole Dexterity bonus to your AC.
Sometimes you can’t use your Dexterity bonus (if you have one). If you can’t react to a blow, you can’t use your Dexterity bonus to AC. (If you don’t have a Dexterity bonus, nothing happens.)
Many other factors modify your AC.
Enhancement effects make your armor better.
Magical deflection effects ward off attacks and improve your AC.
Natural armor improves your AC.
Some other AC bonuses represent actively avoiding blows. These bonuses are called dodge bonuses. Any situation that denies you your Dexterity bonus also denies you dodge bonuses. (Wearing armor, however, does not limit these bonuses the way it limits a Dexterity bonus to AC.) Unlike most sorts of bonuses, dodge bonuses stack with each other.
Some attacks disregard armor, including shields and natural armor. In these cases, the attacker makes a touch attack roll (either ranged or melee). When you are the target of a touch attack, your AC doesn’t include any armor bonus, shield bonus, or natural armor bonus. All other modifiers, such as your size modifier, Dexterity modifier, and deflection bonus (if any) apply normally.
Your speed tells you how far you can move in a round and still do something, such as attack or cast a spell. Your speed depends mostly on your race and what armor you’re wearing.
Dwarves, gnomes, and halflings have a speed of 20 feet (4 squares), or 15 feet (3 squares) when wearing medium or heavy armor (except for dwarves, who move 20 feet in any armor).
Humans, elves, half-elves, and half-orcs have a speed of 30 feet (6 squares), or 20 feet (4 squares) in medium or heavy armor.
If you use two move actions in a round (sometimes called a "double move" action), you can move up to double your speed. If you spend the entire round to run all out, you can move up to quadruple your speed (or triple if you are in heavy armor).
Generally, when you are subject to an unusual or magical attack, you get a saving throw to avoid or reduce the effect. Like an attack roll, a saving throw is a d20 roll plus a bonus based on your class, level, and an ability score. Your saving throw modifier is:
Base save bonus + ability modifier
Base Save Bonus
A saving throw modifier derived from character class and level. Base save bonuses increase at different rates for different character classes. Base save bonuses gained from different classes, such as when a character is a multiclass character, stack.
Saving Throw Types
The three different kinds of saving throws are Fortitude, Reflex, and Will:
These saves measure your ability to stand up to physical punishment or attacks against your vitality and health. Apply your Constitution modifier to your Fortitude saving throws.
These saves test your ability to dodge area attacks. Apply your Dexterity modifier to your Reflex saving throws.
These saves reflect your resistance to mental influence as well as many magical effects. Apply your Wisdom modifier to your Will saving throws.
Saving Throw Difficulty Class
The DC for a save is determined by the attack itself.
Automatic Failures and Successes
A natural 1 (the d20 comes up 1) on a saving throw is always a failure (and may cause damage to exposed items; see Items Surviving after a Saving Throw). A natural 20 (the d20 comes up 20) is always a success.