What are the ability modifiers (other than Dex) that can be used when calculating AC?

Question

As far as my knowledge of D&D goes there are 2 ways to determine AC:

1. Calculation of AC through Base + Stat modifiers

   Examples of these AC calculations are:

   • Unarmored = 10 + Dex mod
   • Unarmored defense, such as Barbarian = 10 + Con mod + Dex mod
   • Light armors, such as Leather Armor = 11 + Dex mod
   • Medium armors, such as Breastplate = + Dex mod (max 2)
   • Spells, such as Mage Armor (AC = 13 + Dex mod)

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2. Setting the base AC to a specific value

   Examples of these AC calculations are:

   • Heavy Armor, such as Plate Armor = 18
   • Racial, such as Tortle's Natural armor race = 17
   • Spells such as Barkskin = 16

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My interest goes out to the first way of calculating AC.

What are the stat modifiers (other than Dex) that can be used when calculating AC?

I already found 2:

• Barbarian's Unarmored Defense = 10 + DEX mod + CON mod
• Monk's Unarmored Defense = 10 + DEX mod + WIS mod

Are there any others that I missed?

Answer 1

Dexterity, Constitution, and Wisdom can be added permanently to AC. Intelligence can be added for a minute. Charisma can be added through a magic item from Hoard of the Dragon Queen or to a single attack. I found no way at all to add Strength to AC.

Below I will provide "the best" methods of adding a given ability modifier to one's Armor Class. By "best" I mean the one that lasts the longest, which, in the case of Charisma, is quite short. This means that features which add Constitution to AC for 1 attack, turn, round, minute, or anything else will not be mentioned/listed:

Barbarian's Unarmored Defense feature (Con and Dex):

While you are not wearing any armor, your Armor Class equals 10 + your Dexterity modifier + your Constitution modifier. You can use a shield and still gain this benefit.

- Player's Handbook (page 48)

Monk's Unarmored Defense feature (Wis and Dex):

Beginning at 1st level, while you are wearing no armor and not wielding a shield, your AC equals 10 + your Dexterity modifier + your Wisdom modifier.

- Player's Handbook (page 78)

Bladesinging Wizard's Bladesong feature (Int):

[...] You can use a bonus action to start the Bladesong, which lasts for 1 minute. It ends early if you are incapacitated, if you don medium or heavy armor or a shield, or if you use two hands to make an attack with a weapon. You can also dismiss Bladesong at any time you choose (no action required).

While your bladesong is active, you gain the following benefits:

• You gain a bonus to your AC equal to your Intelligence modifier (minimum of +1) [...]

- Sword Coast Adventurer's Guide (page 143)

Unearthed Arcana's Oath of Heroism Paladin's Glorious Defense feature (Cha):

[...] When a creature you can see hits you with an attack roll, you can use your reaction to gain a bonus to AC against that attack, potentially causing it to miss you. The bonus equals your Charisma modifier (minimum of +1) [...]

- Bard and Paladin Unearthed Arcana (page 2) [link to document]

An item from Hoard of the Dragon Queen (Cha):

This item is the Black Dragon Mask which has the following property:
Draconic Mastery. While you are wearing no armor, you can add your Charisma bonus to your Armor Class.

Thanks to user David Coffron for pointing out this item!