List of features and items that affect AC

Class features

Feature	AC bonus	Class (Level)	Notes
Armour of the Swarm	+2	Swarmkeeper Ranger (11)	Applies for one turn after using Mighty Teleport.
Bladesong	+2 to +4	Bladesinger (2)	Applies while Bladesinging. Bonus starts at +2 and increases to +3 at level 5 and +4 at level 9.
Defence (fighting style)	+1	Fighter (1), Ranger (2), Paladin (2)	Applies while wearing any armour
Defensive Flourish	+4	College of Swords Bard (3)	Applies for one turn after striking a target with the flourish.
Draconic Resilience	+3	Draconic Bloodline Sorcerer (3)	Equivalent to  Mage Armour. Only applies while unarmoured. Affects base AC and does not stack with other effects that change base AC.
Unarmoured Defence (Barbarian)	+CON modifier	Barbarian (1)	Only applies while unarmoured. Affects base AC and does not stack with other effects that change base AC.
Unarmoured Defence (Monk)	+WIS modifier	Monk (1)	Only applies while unarmoured and not wearing a shield. Affects base AC and does not stack with other effects that change base AC.
Wild Magic: Protective Lights	+1	Wild Magic Barbarian (3)	One of eight possible wild magic effects applied during  Rage: Wild Magic. Affects the barbarian and all allies in 3 m / 10 ft.
Wild Shape	Varies	Druid (2)	While wild shaped, you take on the base AC of the form. This does not stack with other effects that change base AC. For a list of the base ACs of wild shape forms, see this list.

Feats

Feat	AC bonus	Notes
Defensive Duellist	+Proficiency bonus	Applies to a single incoming melee attack at the cost of a  Reaction.
Dual Wielder	+1	Applies while dual wielding.
Magic Initiate: Cleric	+1 (potentially)	Increases maximum Dexterity bonus to AC while wearing medium armour from +2 to +3. This is the same as Medium Armour Master and likely is not intended to be part of this feat.
Medium Armour Master	+1 (potentially)	Increases maximum Dexterity bonus to AC while wearing medium armour from +2 to +3.

Spells

Spell	AC bonus	Duration	Concentration	Affects	Notes
Barkskin	Sets AC to 16	Until long rest	Yes	Self or allies	Has no effect if the target has an AC higher than 16.
Haste	+2	10 rounds	Yes	Self or allies
Mage Armour	+3	Until long rest	No	Self or allies	Only works while unarmoured. Affects base AC and does not stack with other effects that change base AC.
Mirror Image	+3 to +9	10 rounds (or until depleted)	No	Self	Starts at 3 mirror images for +9 AC. Each missed attack will remove one mirror image and reduce the AC bonus by 3.
Shield	+5	Until the start of your next turn	No	Self	Cast as a reaction
Shield of Faith	+2	Until long rest	Yes	Self or allies
Warding Bond	+1	Until long rest	No	Allies

Equipment types

Type	AC bonus	Notes
Light Armour	Varies	Light armours typically have AC values of 11 to 14. See Light Armour for a comprehensive list.
Medium Armour	Varies	Medium armours typically have AC values of 13 to 17, but cap the AC bonus from Dexterity to +2. This cap can be increased to +3 with  Medium Armour Master and armours with the Exotic Material property do not have this cap. See Medium Armour for a comprehensive list.
Heavy Armour	Varies	Heavy armours typically have AC values of 16 to 21, but do not get any AC bonus from Dexterity. A negative Dexterity modifier will still apply, however. See Heavy Armour for a comprehensive list.
Shields	+1 to +3	Most shields grant +2 AC. See Shields for a comprehensive list.

Equipment

Item	AC bonus	Notes	Found in Act
Armour of Moonbasking	+2	Applies while wild shaped as well. For Circle of the Stars druids in a  Starry Form, the bonus is actually applied twice for +4 AC.	3
Bloodthirst	+1	Applies when equipped in the off-hand only.	3
Bonespike Boots	+1	Only applies while unarmoured and not wielding a shield.	3
Bracers of Defence	+2	Only applies while unarmoured and not wielding a shield.	1
Bracing Band	+1	Applies for one turn after pushing an enemy. This can be triggered by any push, not just  Shove.	1
Cloak of Protection	+1		2
Cloth of Authority	+1		3
Cold Snap	+1	Applies when equipped in the off-hand only.	3
Defender Flail	+1		1
Defender Greataxe	+1	When making an attack, can choose to reduce the weapon enchantment by 1 to gain +1 AC for 1 round.	2
Evasive Shoes	+1		2
Garb of the Land and Sky	+1		3
Gleamdance Dagger	+1	Applies when equipped in the off-hand only.	3
Helm of Balduran	+1		3
Infernal Robe	+1		3
Mutilated Carapace	+1		3
Potent Robe	+1		2
The Protecty Sparkswall	+1	While any  Lightning Charges are active.	1
Ring of Protection	+1		1
Ring of Twilight	+1	AC bonus only applies while obscured.	2
Robe of Supreme Defences	+1	Applies while concentrating.	3
Robe of the Weave	+2		3
Shield of Scorching Reprisal	+1	For 4 turns after using  Blazing Retaliation.	2
Vest of Soul Rejuvenation	+2		3
Viconia's Priestess Robe	+1		3
Wavemother's Cloak	+2	Bonus is granted at the start of each turn while in combat. It is removed when taking damage.	3
Wavemother's Robe	+1		3
Wondrous Gloves	+1		1

Consumables

Type	AC bonus	Duration	Notes
Potion of Speed	+2	3 turns	Does not stack with any other source of  Hastened.
Terazul	+2	2 turns	Stack with any other source of  Hastened.

Conditions and features that give penalty to AC

Item or Feature	AC penalty
Acid	-2
Dazed	Dexterity bonus
Houndmaster's Prey	-3
Mindsteal Link	-2
Mud-Drenched	-2
Shred Armour	-2
Slow	-2
Spindleweb Skepticism	-6