This is a description of the Armor Class values found in Inventory and Record screens, and how to interpret them. Let me know what you think.
Armors offer different levels of protection against each of the four types of physical damage. This means that each character has four Armor Classes, one against each type of damage. For instance, a warrior with 16 Dexterity in full plate has an AC of -1 against crushing damage, -5 against slashing damage, and -4 against piercing and missile damage. However, the game doesn't display these values anywhere. In order to know the ACs of your characters you need to calculate them from the AC values the game actually displays, which can be quite confusing.
The game displays AC values in three areas:
- The Inventory screen: The AC values are located in the armor class section, which comprises the minipanel located at the top right corner of the Inventory and the shield icon besides this minipanel.
- The Character Record displays AC values in two of its tabs:
- The Information tab: The values displayed here are very incomplete or missing altogether, so you want to skip this tab when it comes to AC.
- The Combat stats tab: The AC values are in the second group of stats displayed here. These are exactly the same as the values displayed in the Inventory screen. The only difference is that for some reason this tab displays the AC modifiers (see below) twice.
These AC values can be divided into four groups: Displayed AC, AC modifiers, armor and AC bonuses. Most of these values don't have a meaning, but are still useful to determine the ACs of a character. The rest of this discussion explains how to do that.
I call the first value in the list Displayed AC. In the Inventory screen this value is displayed on the shield icon. The Displayed AC doesn’t have a meaning, it is just a number the game uses to calculate each of the four actual armor classes.
Apart from the Displayed AC, the game uses four other values, called Armor Class modifiers, or AC modifiers for short, to calculate each armor class. The four AC modifiers are: AC modifier vs. piercing, AC modifier vs. slashing, AC modifier vs. crushing, and AC modifier vs. missile; i. e., there is an AC modifier for each type of weapon damage. The game calculates each armor class by adding up the Displayed AC and the AC modifier for the relevant type of damage. For example, the AC against slashing damage is the result of adding up the Displayed AC and the AC modifier against slashing.
Just like the Displayed AC, the AC modifiers don’t have a meaning, they are just numbers the game uses to get the actual ACs. Their values are also in the Inventory screen, at the bottom of the Armor Class minipanel.
In the example of the picture the Displayed AC character is -4, and the AC modifiers are: -4 vs. Crushing, ; -8 vs. Missile, -3 vs. Piercing, and -4 vs. Slashing. This means that the actual four armor classes are:
- AC vs. crushing weapons: -4 -4 = -8.
- AC vs. slashing weapons: -4 -8 = -12.
- AC vs. piercing weapons: -4 -3 = -7.
- AC vs. missile weapons: -4 -4 = -8.
Not all the AC modifiers have to be listed. When the modifier against a type of damage is missing it means that it’s value is 0, i. e, the AC against that type of damage is the Displayed AC. Depending on the gear and the magical protections of a character, its AC modifiers section can list any number of values, from none to all four of them.HOW THE GAME CALCULATES THESE VALUESThis is a discussion of how the game comes up with the values it shows for the Displayed AC and the AC modifiers. I've put it in a spoiler section because it doesn't add new information, it just explains where these values come from.
TYPES OF AC PROTECTIONS
The origin of the Displayed AC number is related to the way armors are described. The descriptions of armors list several values for their AC: one first “main” value followed by one or more values in parenthesis. For example, the description of full plate says “Armor class: 1 (-3 vs. Slashing, -2 vs. Piercing or Missile)”. However, the meaning of that “main” AC value is not fixed, it means something different for each type of armor. For instance, in the case of full plate mail the “main” AC value is the AC against crushing damage, but in the case of plate mail it is the AC against crushing, piercing and missile damage. You can figure out the meaning of the “main” AC value by elimination: It is the AC or ACs against the type of damage NOT mentioned in the parenthesis. For example, the description of the full plate mail mentions in the parenthesis the ACs against slashing, piercing and missiles. Therefore, its “main” AC is against crushing weapons.
These are the meanings of the "main" AC value in the description of each kind of armor:
- Leather armor: AC vs. crushing and slashing
- Studded leather armor: AC vs. crushing
- Hide armor: AC vs. crushing and slashing
- Chain mail: AC vs. piercing and missile
- Splint mail: AC vs. slashing
- Plate mail: AC vs. crushing, piercing and missile
- Full plate mail: AC vs. crushing
When a character wears an armor, the game uses the “main” value of that armor as a base to calculate the Displayed AC for that character. The Displayed AC is the result of adding up the “main” value of the armor and all the AC modifications that apply to all the ACs. These include Dexterity modifications, bonuses obtained through rings and amulets, etc.
The AC modifiers are the difference between each of the four actual ACs and the Displayed AC.EXAMPLE
Minsc is wearing a full plate mail. As seen above, the “main” AC value of the full plate mail is 1 against crushing weapons. Minsc’s Dexterity (16) gives him a -2 bonus to his AC. The Dexterity bonus applies to all the ACs, so the game uses it to calculate his Displayed AC: Displayed AC = 1 - 2 = -1.
The four ACs of Minsc are the result of adding up his Dexterity bonus to the ACs provided by the full plate mail:
- AC vs. crushing weapons: 1 - 2 = -1.
- AC vs. slashing weapons: -3 - 2 = -5.
- AC vs. piercing weapons: -2 - 2 = -4.
- AC vs. missile weapons: -2 - 2 = -4.
The AC modifiers are the difference between each of these four ACs and the Displayed AC, which is -1.
- Crushing: No difference, so it is not in the list.
- Slashing: -5 - (-1) = -4.
- Piercing: -4 - (-1) = -3.
- Missile: -4 - (-1) = -3.
Now Minsc puts on the Senses of the Cat, a pair of boots that provide a -5 bonus to his AC against missile damage. His new AC against missile damage is: -4 -5 = -9. Since this bonus doesn’t apply to all types of damage, it doesn’t affect the Displayed AC, which remains at -1. The new AC modifier against missile is -9 - (-1) = -8.
Finally, Minsc puts on the Destroyer of the Hills, a belt that gives him a -4 bonus against crushing damage. Again, this doesn’t affect his Displayed AC because this bonus doesn’t apply to all types of damage. The final ACs of Minsc are:
- AC vs. crushing weapons: -1 - 4 = -5.
- AC vs. slashing weapons: -5.
- AC vs. piercing weapons: -4.
- AC vs. missile weapons: -9.
The values shown in the game for these ACs are:
- Displayed AC: -1.
- AC modifier vs. Crushing: -5 - (-1) = -4.
- AC modifier vs. Slashing: -5 - (-1) = -4.
- AC modifier vs. Piercing: -4 - (-1) = -3.
- AC modifier vs. Missile: -9 - (-1) = -8.
AC protections can be divided in several types:
- Protections that set all the ACs to a certain value. These include armors, bracelets, spells, potions, and the AC of monks. When a character uses two protections of this type, only the better one has effect.
Example: a mage wears magical bracelets that set her ACs to 8. Before she enters a dungeon she casts the spell Ghost Armor, which sets her ACs to 2. For the duration of the spell her ACs stay at 2 and the effect of the bracelet is ignored. When the duration of Ghost Armor expires, her ACs go back to 8.
- Protections that give a bonus to one or more ACs. For example, the spell Blur improves all the ACs by 3 points. These can be further subdivided in three types:
• Protections that give bonuses to all ACs. These include shields, rings, amulets, spells, abilities, class kit bonuses, the Dexterity score, and the single weapon proficiency. These bonuses change the Displayed AC.
• Protections that only give a bonus to one AC: These include belts, boots and robes. These bonuses change the AC modifiers.
• Protections that apply conditionally. An example is the Protection from Evil spell, that applies a -2 adjustment to all the ACs when something evil attacks you. The effect of these protections is not reflected in any of the AC values show in the UI.
Apart from this, some negative effects apply penalties that affect all armor classes. For example, blindness applies a +4 penalty.