Ad placeholder

Armour Class

From bg3.wiki
(Redirected from AC)
Jump to navigation Jump to search

Armour Class (AC) is a measurement of how difficult a creature is to be hit by an attack. In order to successfully hit a creature, the results of an attack roll must have a number equal to or greater than the target's Armour Class. AC can be increased by equipping armour and shields, by selecting certain feats when leveling up, or utilizing certain spells.

Formulas[edit | edit source]

The default formula that determines AC is:

10 + Dexterity modifier + armour bonus + shield bonus + other bonuses and penalties

Medium armour caps the Dexterity Modifier to +2.[1][2] Heavy armour ignores the modifier entirely.

Shields will grant the listed AC bonus to whoever equips them, regardless of which weapon slot they are currently using.

Other formulas[edit | edit source]

Unarmoured creatures may use one of the following different formulas if they have certain features. Creatures always use whichever formula would result in a higher AC among those they have access to.[3]

Mage Armour Mage Armour or Draconic Resilience Draconic Resilience:

13 + Dexterity modifier + shield bonus + other bonuses and penalties

Unarmoured Defence (Barbarian) Unarmoured Defence (Barbarian):

10 + Constitution modifier + Dexterity modifier + shield bonus + other bonuses and penalties

Unarmoured Defence (Monk) Unarmoured Defence (Monk):

10 + Wisdom modifier + Dexterity modifier + other bonuses and penalties

Mathematics[edit | edit source]

Armour Class becomes more useful the greater it is; for instance, the difference in effectiveness between 20 and 19 AC is greater than the difference in effectiveness between 16 and 15.

To illustrate this, if a defender has 15 AC and 10 HP, and the attacker has +4 (50% chance to hit) to attack rolls, and deals 2 damage per attack, the defender would on average survive for 10 turns.

If the defender's AC was increased to 16 (45% chance to be hit), they would instead survive for an average of 11.1 rounds (an 11% increase in effectiveness).

Meanwhile, if the defender has 19 AC (30% chance to be hit), they would survive for an average of 16.66 rounds. If their AC was increased to 20 (25% chance to be hit), they would be able to survive for an average of 20 rounds (a 20% increase in effectiveness).

The difference between 25 and 24 is even greater, with a 100% increase in effectiveness (50 vs 100 rounds).

Items increasing Armour Class[edit | edit source]

Equipment Slot AC Increase Effect Found in Act
Armour of Agility Armour Armour 17
+ Full Dexterity Dexterity Modifier
Exotic Material
Add your full Dexterity Modifier to your Armour Class Armour Class. Additionally, this armour does not impose Disadvantage Icon.png Disadvantage on Stealth Ability Checks.

Saving throws +2

3
Armour of Moonbasking Armour Armour 11
+Dexterity Dexterity Modifier
+ 2 (Bonus)
Lunar Bestial Vitality
You gain HP Icon.png 22 temporary hit points after casting Wild Shape Wild Shape. While those temporary hit points are active reduce all incoming damage by 1.
Lunar Bestial Fortitude
You have a +2 bonus to Armour Class Armour Class. You also have Advantage Icon.png Advantage on Saving throws against spells. This effect persists while using your druidic Wild Shape Wild Shape ability.
3
Bonespike Boots Footwear Footwear +1

Brutal Leap Brutal Leap

Evasive Instinct
You have a +1 bonus to Armour Class Armour Class and Saving throws as long as you are not wearing armour or holding a shield.
Refined Vaulting
Jump Jump distance is increased by 1.5 m / 5 ft.
3
Bracers of Defence Gloves Gloves +2
Become the Bulwark
You gain a +2 bonus to Armour Class Armour Class as long as you are not wearing armour or holding a shield.
1
Bracing Band Ring Ring +1
Personal Space
After shoving an enemy[See Notes], the wearer gains a +1 to their Armour Class Armour Class until their next turn.
1
Cloak of Protection Cloak Cloak +1 Armour Class +1

Saving throw +1

2
Defender Flail Main Hand Melee Main Hand Melee +1
Steel Physiology
Reduce incoming Damage TypesBludgeoning, Damage TypesPiercing, and Damage TypesSlashing damage by 1.

Armour Class +1

2
Evasive Shoes Footwear Footwear +1 Acrobatics +1

Armour Class +1

2
Helm of Balduran Headgear Headgear +1

Attackers can't land Critical Hits on the wearer.

Balduran's Vitality
The helmet heals you 2hit points at the beginning of every turn.
Balduran's Favour
You have a +1 bonus to Armour Class Armour Class and Saving throws.
Stun Immunity
You can't be Stunned Stunned.
3
Ring of Protection Ring Ring +1 Armour Class +1

Saving throw +1

1
Ring of Twilight Ring Ring +1, only while at least Lightly Obscured Lightly Obscured
Treader by Twilight
You gain a +1 bonus to Armour Class Armour Class while obscured.
2
Sharpened Snare Cuirass Armour Armour 14
+ Full Dexterity Dexterity Modifier
Exotic Material
Add your full Dexterity Modifier to your Armour Class Armour Class. Additionally, this armour does not impose Disadvantage Icon.png Disadvantage on Stealth Ability Checks.
Sharpened Snare
Creatures have Disadvantage Icon.png Disadvantage on Saving throws when resisting your attacks and spells that inflict Restrained Restrained.
2
Unwanted Masterwork Scalemail Armour Armour 16
+ Full Dexterity Dexterity Modifier

Resistance to Damage TypesFire damage.

Exotic Material
Add your full Dexterity Modifier to your Armour Class Armour Class. Additionally, this armour does not impose Disadvantage Icon.png Disadvantage on Stealth Ability Checks.
3
Wondrous Gloves Gloves Gloves +1
Troubadour's Wonder
Your Armour Class Armour Class increases by 1. In addition, if you have Bardic Inspiration Bardic Inspiration, you gain 1 more use of it.
1
Yuan-Ti Scale Mail Armour Armour 15
+ Full Dexterity Dexterity Modifier
Exotic Material
Add your full Dexterity Modifier to your Armour Class Armour Class. Additionally, this armour does not impose Disadvantage Icon.png Disadvantage on Stealth Ability Checks.
Ambusher
Gain a +1 bonus to Initiative Rolls Initiative Rolls.
2

Notes[edit | edit source]

  1. The Medium Armour Master feat increases the cap from +2 to +3.
  2. Four rare armours have an "Exotic Material" trait that allow the wearer to get the full Dexterity bonus to AC, namely Yuan-Ti Scale Mail, Unwanted Masterwork Scalemail, Sharpened Snare Cuirass, and Armour of Agility.
  3. Alternative formulas are only used if no items are worn in the chest, hands, helm or boots slots which are labelled as armour. The Monk version also stops working if a shield is carried.