Armor Class

Armor Class (AC) is the character stat that determines the chance to avoid being hit by a physical attack.

How it works

A character's AC score is a number between 20 and -20: The lower, the better.

Each time a character is attacked using a physical weapon, the target's AC score is compared to the attacker's attack roll and THAC0. The attack only "hits" the target if:

Attack roll ≥ THAC0 - AC

Note that even if an attack "hits", other defenses (such as Damage Resistance) can still negate or reduce the damage inflicted.

AC score

The effective AC score that gets used during attacks, is calculated like this:

    base AC
  + general AC modifiers
  + dexterity modifier
  + weapon proficiency bonus

Base AC

The base AC is typically determined by a character's armor. Heavier armor typically gives you a better armor class.

General AC modifiers

The Armor Class section in the Inventory window first shows modifiers or bonuses that apply to all types of attacks. But, below these, are also shown important Armor Class Modifiers to notice and understand: those related to the type of attack, which are...

• Crushing
• Missile
• Piercing
• Slashing

These are shown both at the top-right of the Inventory (you may need to scroll down to the bottom of the various AC modifiers) and on the Record window. They allow the player to calculate the actual total AC against different types of attacks (see example below).

Note that conditional bonuses (i.e. bonuses that do not apply to all types of attacks) are not presented on the user-interface. For example, Protection from Evil, which procures a +2 AC bonus versus attacks from evil creatures, will not be shown under the Armor Class bonuses.

Dexterity modifier

Dexterity gives any character you create a bonus or a penalty depending on the score.

Weapon proficiency bonus

This mostly refers to the Sword & Shield Proficiency which improves the character's AC versus missiles (mostly arrows and crossbow bolts).

But also to the Single Weapon Proficiency which gives AC bonuses whenever you are wielding a one-handed weapon and no shield.

AC shown versus Actual armor class

The visible Armor Class number shown in the Inventory considers only bonuses that apply to all types of attacks, such as the base AC of your armor, the Dexterity AC bonus and magic items that give a general AC bonus.

Example : While the game may show an AC of -5 (base armor, Dexterity, etc.) for a given character, a heavy armor may have a Missile modifier of -3, your shield Missile -2 and a Sword and Shield Proficiency an extra Missile -2, for a true AC versus Missile of -12! In addition, spells like Protection from Evil and some Bard songs may improve your AC even further, but will not be shown under the AC section of the Inventory.

Therefore, the general AC shown in the Inventory is often misleading.

Behind the scenes

If you look in the game files, you have column Parameter 1, which is the number and parameter 2 which determine the type of armor class. There six types of armor class.

Param 2 value	Type armor class	Param 2 value	Type armor class
16	Basic armor class.	2	Missiles attack armor class bonus.
8	Slashing attacks armor class bonus.	1	Blunt attacks armor class bonus.
4	Piercing attacks armor class bonus.	0	Armor class bonus.

External links

• Armor Class article on the Baldur's Gate Wiki, a wiki for the Baldur's Gate games.