d20 LogoSystem Reference Document v3.5



Combat is cyclical; everybody acts in turn in a regular cycle of rounds. Combat follows this sequence:

  1. Each combatant starts out flat-footed. Once a combatant acts, he or she is no longer flat-footed.

  2. Determine which characters are aware of their opponents at the start of the battle. If some but not all of the combatants are aware of their opponents, a surprise round happens before regular rounds of combat begin. The combatants who are aware of the opponents can act in the surprise round, so they roll for initiative. In initiative order (highest to lowest), combatants who started the battle aware of their opponents each take one action (either a standard action or a move action) during the surprise round. Combatants who were unaware do not get to act in the surprise round. If no one or everyone starts the battle aware, there is no surprise round.

  3. Combatants who have not yet rolled initiative do so. All combatants are now ready to begin their first regular round of combat.

  4. Combatants act in initiative order (highest to lowest).

  5. When everyone has had a turn, the combatant with the highest initiative acts again, and steps 4 and 5 repeat until combat ends.


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

With a ranged weapon, your attack bonus is:

Base attack bonus + Dexterity modifier + size modifier + range penalty

Table: Size Modifiers

SizeSize ModifierSizeSize Modifier


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.

Minimum Damage: If penalties reduce the damage result to less than 1, a hit still deals 1 point of damage.

Strength Bonus: 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.

Off-Hand Weapon: When you deal damage with a weapon in your off hand, you add only 1/2 your Strength bonus.

Wielding a Weapon Two-Handed: When you deal damage with a weapon that you are wielding two-handed, you add 1-1/2 times your Strength bonus. However, you don’t get this higher Strength bonus when using a light weapon with two hands.

Multiplying Damage: 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.

Ability Damage: 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:

10 + armor bonus + shield bonus + Dexterity modifier + size modifier

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.)

Other Modifiers: Many other factors modify your AC.

Enhancement Bonuses: Enhancement effects make your armor better.

Deflection Bonus: Magical deflection effects ward off attacks and improve your AC.

Natural Armor: Natural armor improves your AC.

Dodge Bonuses: 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.

Touch Attacks: 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.


When your hit point total reaches 0, you’re disabled. When it reaches –1, you’re dying. When it gets to –10, you’re dead.


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

Saving Throw Types: The three different kinds of saving throws are Fortitude, Reflex, and Will:

Fortitude: 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.

Reflex: These saves test your ability to dodge area attacks. Apply your Dexterity modifier to your Reflex saving throws.

Will: 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.