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Understanding Armor Class values

AlonsoAlonso Member Posts: 806
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.
    jiyq4duk5t6l.png
  • 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.
      dhl8bvest1o4.png
    • 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.
      kwm1v38nshbi.png

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.
thq5b3zaq01o.png

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 VALUES

This 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.
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.

TYPES OF AC PROTECTIONS
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.

Post edited by Alonso on
GusindaSkatanhistamiiniJuliusBorisovBelgarathMTHAndreaColomboTimbo0o0o0gorgonzolaGrond0ThanatosZeroSoidoPsicoVic

Comments

  • AlonsoAlonso Member Posts: 806
    Grond0 wrote: »
    that is derived directly from the sum of the adjustments shown (from armor, boots, girdles etc).
    Not sure if I understand. When you talk about "the adjustments shown", do you mean the adjustments shown in the AC section (the lines that say things like "Buckler: -1")? Those adjustments affect the Displayed AC, not the AC modifiers. Or are you talking about something different?
    Grond0 wrote: »
    If you wanted to give more detail...
    I know, it's an incomplete description. I can add what you have written if that's OK with you.

  • Grond0Grond0 Member Posts: 6,995
    Alonso wrote: »
    Grond0 wrote: »
    that is derived directly from the sum of the adjustments shown (from armor, boots, girdles etc).
    Not sure if I understand. When you talk about "the adjustments shown", do you mean the adjustments shown in the AC section (the lines that say things like "Buckler: -1")? Those adjustments affect the Displayed AC, not the AC modifiers. Or are you talking about something different?
    Grond0 wrote: »
    If you wanted to give more detail...
    I know, it's an incomplete description. I can add what you have written if that's OK with you.

    Apologies - that was badly worded. The character record tells you what the sum of the adjustments is for each type of AC modifier, e.g. if you're wearing the Elves Bane girdle, ankheg plate mail and using a large shield the record will show you have a -5 modifier against missiles. The point I was trying to make is that information is available directly rather than needing to work it out indirectly.

    Feel free to write whatever you want. If I disagree with something I might say so in a post, but I'm certainly not going to claim any copyright infringement :p.

    Alonso
  • AlonsoAlonso Member Posts: 806
    Grond0 wrote: »
    The point I was trying to make is that information is available directly rather than needing to work it out indirectly.
    Yeah, that's why I put all of that inside a spoiler section and wrote a note about it before the spoiler section. I guess that note was not very clear, though, so I've added a header and expanded the note to make it more clear. Does it make more sense now?
    Grond0 wrote: »
    Feel free to write whatever you want. If I disagree with something I might say so in a post, but I'm certainly not going to claim any copyright infringement :p.
    Thanks. I've added what you wrote at the end of my first post, although I redacted it a lot and added some more info.

    Grond0
  • Grond0Grond0 Member Posts: 6,995
    Alonso wrote: »
    Grond0 wrote: »
    The point I was trying to make is that information is available directly rather than needing to work it out indirectly.
    Yeah, that's why I put all of that inside a spoiler section and wrote a note about it before the spoiler section. I guess that note was not very clear, though, so I've added a header and expanded the note to make it more clear. Does it make more sense now?

    I understand what it says. To me the explanation seems unnecessarily complex though and doesn't represent how the game actually works - but others may feel differently :p. In your explanation you say "The AC modifiers are the difference between each of the four actual ACs and the Displayed AC" and go on to give a detailed breakdown of that. If I were doing it I would have my starting point along the following lines:
    - Displayed AC is the base that applies to all attacks and is the figure shown as AC in the character record
    - AC modifiers affect the base only against attacks of that particular type and are shown in brackets in the character record after the AC figure
    I would then go on to explain as you have done what the final AC is for each type of attack and how the game arrives at the values shown.

    In relation to this:
    "[*]Protections that set all the ACs to a certain value. These include armors, bracelets, spells, abilities and the single weapon proficiency."
    single weapon proficiency is a modifier rather than setting AC. Off the top of my head I think all abilities are also modifiers though I wouldn't swear to that.

    In relation to this:
    "[*]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, the Dexterity score and some class kit bonuses.
    • Protections that only give a bonus to one AC: These include belts, boots and robes.
    • 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 shown in the AC section.
    [/list]"

    It might be helpful to specify that adjustments in the first category are included in the Displayed AC figure and adjustments in the second category in the modifiers (though that might be repetition if you were to change the way your explanation worked as I set out above).

  • kjeronkjeron Member Posts: 2,318
    Alonso wrote: »
    • Protections that only give a bonus to one AC: These include belts, boots and robes.
    • 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 shown in the AC section.
    These modifiers don't actually affect AC - they affect your opponents attack roll. While the net result is the same, it does affect how it's displayed in the attack roll calculation, as a penalty on the left, rather than increasing the number required on the right.

    Blindness also contributes to generic AC, as a +4 penalty. It's included in the displayed value in the inventory and record screen, but it's not listed in the details.
    Grond0 wrote: »
    single weapon proficiency is a modifier rather than setting AC. Off the top of my head I think all abilities are also modifiers though I wouldn't swear to that.
    The wizard Shield and Armor spells set Base AC, as would any abilities that mimic them.
    Monk AC progression is also a Base AC effect, at least in the current game version.

    Grond0
  • DanacmDanacm Member Posts: 910
    Maybe just use the terms:
    Base Ac (lowering your ac from 10 to the set value. Not stackable with other base ac items and spells.)
    Bonus ac( lowering ac by the value and stackable with other bonus ac sources like single weapon style, rings etc)
    All of theese affects all damage types, and there are also ac items that affects only one dmg type, like crushing, piercing, missiles and slashing.

    Grond0
  • AlonsoAlonso Member Posts: 806
    Grond0 wrote: »
    Displayed AC is the base that applies to all attacks [...] AC modifiers affect the base only against attacks of that particular type
    I thought that this was clear from my description, but it looks like it wasn't, so I have changed it a bit to better convey this. Hope it's more clear now.
    Grond0 wrote: »
    - Displayed AC [...] is the figure shown as AC in the character record
    - AC modifiers [...] are shown in brackets in the character record after the AC figure
    I can't see this in my Record screen. I see a list of AC modifiers, but not the Displayed AC (and no brackets). Which is quite weird, by the way.
    Grond0 wrote: »
    single weapon proficiency is a modifier rather than setting AC. Off the top of my head I think all abilities are also modifiers though I wouldn't swear to that.
    Thanks, I made some mistakes there. Corrected.
    Grond0 wrote: »
    It might be helpful to specify that adjustments in the first category are included in the Displayed AC figure and adjustments in the second category in the modifiers
    Done.

  • AlonsoAlonso Member Posts: 806
    kjeron wrote: »
    These modifiers don't actually affect AC - they affect your opponents attack roll. While the net result is the same, it does affect how it's displayed in the attack roll calculation, as a penalty on the left, rather than increasing the number required on the right.
    Oh, my, it's even more complicated than I thought! Can you give us a couple of examples to clarify this a bit?
    kjeron wrote: »
    Blindness also contributes to generic AC, as a +4 penalty. It's included in the displayed value in the inventory and record screen, but it's not listed in the details.
    Thanks. Added.
    Danacm wrote: »
    Maybe just use the terms:
    Base Ac (lowering your ac from 10 to the set value. Not stackable with other base ac items and spells.)
    Bonus ac( lowering ac by the value and stackable with other bonus ac sources like single weapon style, rings etc)
    All of theese affects all damage types, and there are also ac items that affects only one dmg type, like crushing, piercing, missiles and slashing.
    Not sure what your point is. Can you elaborate?

  • kjeronkjeron Member Posts: 2,318
    edited March 2019
    Alonso wrote: »
    kjeron wrote: »
    These modifiers don't actually affect AC - they affect your opponents attack roll. While the net result is the same, it does affect how it's displayed in the attack roll calculation, as a penalty on the left, rather than increasing the number required on the right.
    Oh, my, it's even more complicated than I thought! Can you give us a couple of examples to clarify this a bit?
    Top attack roll Dorn has just a melee weapon and Destroyer of the Hills belt (-4 vs crushing). Neera gets -4 to her attack roll.
    Bottom attack roll Dorn has nothing equipped except melee weapon. Neera gets +/0 to her attack roll.
    Neera's using a basic quarterstaff for both.
    (Fatigue was set to remove luck penalty).
    hd12yzcdt6ri.png
    Opcode 219 (which provides the effect vs. evil in Protection from Evil) works the same way.
    I have a more detailed explanation about the attack roll here

    Grond0Alonso
  • Grond0Grond0 Member Posts: 6,995
    Alonso wrote: »
    Grond0 wrote: »
    - Displayed AC [...] is the figure shown as AC in the character record
    - AC modifiers [...] are shown in brackets in the character record after the AC figure
    I can't see this in my Record screen. I see a list of AC modifiers, but not the Displayed AC (and no brackets). Which is quite weird, by the way.

    I agree it's confusing as the same information is shown several times in the Character Record, but not in a consistent fashion. I was referring to this within the combat stats section of the record:
    7cptlt7ahsbk.jpg

  • AlonsoAlonso Member Posts: 806
    edited March 2019
    @kjeron: Thank you, I think I get it now. But that seems to be a bug, or a design mistake. All the item descriptions and the game UI agree that these values affect the AC of the character who wears the items, not the attack roll of his enemy. Which makes sense.

    @Grond0: Nevermind, mistake.

    Post edited by Alonso on
  • kjeronkjeron Member Posts: 2,318
    The two of you are looking at different tabs, "Information" tab and "Combat Stats" tab.

    Alonso
  • AlonsoAlonso Member Posts: 806
    Ooops, as kjeron said, I was looking at the wrong tab. Partly because, as Grond0 said, that info is repeated several times across the tabs in the Character Record.

    Anyway, I've added a new section at the beginning with some pictures to clarify which are the values we are discussing.

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