How To Calculate Armour Class

Calculate your character’s Armour Class in Dungeons & Dragons 5th Edition with this comprehensive tool. Includes base AC, armor bonuses, shields, Dexterity modifiers, and magical enhancements.

Comprehensive Guide to Calculating Armour Class in D&D 5e

Armour Class (AC) represents your character’s ability to avoid being hit by attacks in Dungeons & Dragons 5th Edition. Understanding how to calculate AC properly is crucial for both players and Dungeon Masters, as it directly impacts combat survival and effectiveness.

Core Components of Armour Class

Your AC is determined by several potential factors:

1. Base AC from Armor: The foundation of your AC comes from whatever armor you’re wearing (or not wearing).
2. Dexterity Modifier: Most armor types add your Dexterity modifier to your AC, though heavy armors impose limits.
3. Shield Bonus: Using a shield typically adds +2 to your AC.
4. Magic Bonuses: Enchanted armor, shields, or items like cloaks of protection can increase your AC.
5. Natural Armor: Some class features (like a Barbarian’s Unarmored Defense) or monster traits provide natural armor.
6. Other Modifiers: Situational bonuses from cover, spells, or special abilities.

Armor Types and Their AC Calculations

Armor Type	Base AC	Dex Bonus	Strength Requirement	Stealth Disadvantage	Weight
No Armor	10	Full Dex	—	No	—
Padded	11	Full Dex	—	Yes	8 lb.
Leather	11	Full Dex	—	No	10 lb.
Studded Leather	12	Full Dex	—	No	13 lb.
Hide	12	Max +2	—	No	12 lb.
Chain Shirt	13	Max +2	—	No	20 lb.
Scale Mail	14	Max +2	—	Yes	45 lb.
Breastplate	14	Max +2	—	No	20 lb.
Half Plate	15	Max +2	—	Yes	40 lb.
Ring Mail	14	None	—	Yes	40 lb.
Chain Mail	16	None	13 Str	Yes	55 lb.
Splint	17	None	15 Str	Yes	60 lb.
Plate	18	None	15 Str	Yes	65 lb.

Special AC Calculations

Several classes and features provide alternative ways to calculate AC:

• Unarmored Defense (Barbarian/Monk): AC = 10 + Dex modifier + Con modifier (Barbarian) or Wis modifier (Monk)
• Mage Armor: AC = 13 + Dex modifier (no armor required)
• Dragonhide Armor: AC = 13 + Dex modifier (max +2)
• Celestial Armor: AC = 15 + Dex modifier
• Natural Armor (Druid): AC = 10 + Dex modifier + Wis modifier (when not wearing metal armor)

Shields and Their Impact on AC

Shields provide a simple +2 bonus to AC in most cases. The standard shield is the most common, but there are variations:

Shield Type	AC Bonus	Weight	Cost	Special Properties
Shield	+2	6 lb.	10 gp	Standard wooden or metal shield
Buckler	+1	2 lb.	5 gp	Small shield that doesn’t impose disadvantage on Stealth
Shield, +1	+3	6 lb.	1,010 gp	Magical bonus included
Shield, +2	+4	6 lb.	5,010 gp	Magical bonus included
Shield, +3	+5	6 lb.	25,010 gp	Magical bonus included
Animated Shield	Varies	—	—	Floats near you, counts as armor not shield

Magic Items That Enhance AC

Numerous magical items can improve your AC beyond standard armor and shields:

• Cloak of Protection: +1 to AC and saving throws
• Ring of Protection: +1 to AC and saving throws
• Amuleth of the Devout: +1 to AC (cleric/paladin only)
• Bracers of Defense: +2 to AC (while not wearing armor or using a shield)
• Dwarven Plate: AC 18, but doesn’t impose Stealth disadvantage
• Elven Chain: AC 16 + Dex (max +2), considered light armor
• Adamantine Armor: Critical hits become normal hits
• Mithral Armor: Removes Stealth disadvantage and Strength requirements

Common Mistakes in AC Calculation

Avoid these frequent errors when determining your character’s AC:

1. Ignoring Dexterity Caps: Heavy armor provides no Dex bonus, medium armor caps at +2.
2. Double-Counting Bonuses: You can’t stack multiple cloaks of protection for example.
3. Forgetting Shield Bonuses: Many players overlook the +2 from shields in calculations.
4. Miscounting Magic Bonuses: A +1 shield and +1 armor stack for +2 total, not +1.
5. Overlooking Class Features: Monks and Barbarians often forget their Unarmored Defense.
6. Misapplying Cover Bonuses: Cover provides situational bonuses, not permanent AC increases.
7. Incorrect Armor Proficiency: Wearing armor without proficiency imposes penalties.

Optimizing Your Armour Class

To maximize your AC, consider these strategies:

• For Dexterity-Based Characters: Studded leather (+2 Dex) + shield (+2) + magic bonuses can reach AC 20+ with high Dex.
• For Strength-Based Characters: Plate armor (AC 18) + shield (+2) + magic bonuses can reach AC 22+.
• For Spellcasters: Mage Armor (AC 13 + Dex) + shield (+2) is often optimal.
• For Monks/Barbarians: Maximize Wis/Con for Unarmored Defense, consider magic items that don’t require armor.
• For Multiclass Characters: Combine class features (like Monk’s Unarmored Defense with Fighter’s armor proficiencies).

AC in Different Combat Scenarios

Your effective AC can change based on combat conditions:

• Against Ranged Attacks: Cover provides additional AC bonuses (+2 for half cover, +5 for three-quarters cover).
• Against Melee Attacks: Some features (like the Dodge action) impose disadvantage on attacks against you.
• Against Specific Damage Types: Some armors provide resistance to certain damage types (e.g., adamantine against critical hits).
• While Prone: Ranged attacks have disadvantage, melee attacks have advantage (effectively ±5 to hit).
• While Restrained: Attackers have advantage (+5 to hit effectively).

Historical Context of Armor

The armor systems in D&D draw inspiration from historical armor types, though simplified for gameplay. Understanding the real-world counterparts can enhance immersion:

• Padded/Leather: Representing gambesons and simple leather armor used by common soldiers.
• Chain Mail: Based on the interlinked rings that were dominant in medieval Europe from the 3rd century BC to the 16th century AD.
• Plate Armor: Full plate armor developed in the late Middle Ages (14th-15th centuries) and was highly effective against both slashing and piercing weapons.
• Shields: Ranged from small bucklers to large kite shields, often made of wood covered with leather or metal.

For more historical context on armor development, the Metropolitan Museum of Art’s Arms and Armor collection provides excellent resources on medieval and Renaissance armor.

Mathematical Probability of AC

The effectiveness of your AC can be understood through probability. In D&D 5e:

• An AC of 15 means an attacker needs to roll 10+ on a d20 to hit with a +5 attack bonus (50% chance).
• An AC of 20 means the same attacker needs 15+ (30% chance).
• Against a +10 attack bonus (typical for high-level monsters), AC 20 drops to 25% chance to hit.
• Each +1 to AC reduces the chance to be hit by about 5% against most attackers.

This probability curve explains why high-AC builds are so valuable in high-level play, where monster attack bonuses can reach +10 or higher.

AC in Different D&D Editions

Armour Class has evolved across D&D editions:

• Original D&D (1974): AC started at 9 (unarmored) and went down to -10 (best armor). Lower was better.
• AD&D (1977): Similar descending AC system, with more granular armor types.
• D&D 3rd Edition (2000): Introduced ascending AC (higher is better), with base 10 for unarmored.
• D&D 4th Edition (2008): AC became one of several defenses (along with Fortitude, Reflex, Will).
• D&D 5th Edition (2014): Returned to the 3e ascending AC system with simplified calculations.

The current 5e system strikes a balance between simplicity and tactical depth, making AC calculations accessible while maintaining strategic importance.

Homebrew and Variant AC Rules

Many DMs implement house rules for AC. Common variants include:

• Armor as Damage Reduction: Instead of affecting to-hit rolls, armor reduces damage taken.
• Location-Based AC: Different AC values for different body parts (e.g., head, torso, legs).
• Armor Degredation: Armor loses effectiveness as it takes damage in combat.
• Encumbrance Effects: Heavy armor imposes movement penalties or skill check disadvantages.
• Material Matters: Different armor materials provide resistances to specific damage types.

When considering homebrew rules, it’s important to maintain game balance. The official D&D 5e resources provide guidance on maintaining balance when modifying rules.

AC in Other Tabletop RPGs

Different RPG systems handle defense mechanics differently:

• Pathfinder: Similar to D&D 3.5/5e but with more granular armor properties.
• GURPS: Uses Defense Rolls where characters actively dodge or block attacks.
• Shadowrun: Combines armor ratings with soak tests against damage.
• Warhammer Fantasy: Uses a descending AC system similar to early D&D.
• FATE: Uses a narrative approach where defense is more about aspect invocation than fixed numbers.

Understanding these different systems can provide perspective on how D&D’s AC system compares to other game mechanics.

Psychological Impact of High AC

Beyond the mechanical benefits, high AC has psychological effects in gameplay:

• Player Confidence: High AC characters often take more risks in combat.
• DM Challenge: Forces creative solutions beyond simple attacks.
• Resource Management: Encourages enemies to use spells/abilities that target saves rather than attack rolls.
• Tactical Positioning: High-AC characters often draw aggro to protect squishier allies.
• Narrative Impact: A heavily armored knight feels different from a nimble rogue in how they avoid damage.

These psychological factors make AC more than just a number—it shapes playstyle and character identity.

Advanced AC Tactics

Experienced players use these tactics to maximize AC effectiveness:

1. Stacking Bonuses: Combine armor, shield, and magic items that don’t overlap (e.g., +1 armor and cloak of protection).
2. Situational Awareness: Use cover and the Dodge action when expecting heavy attacks.
3. Debuff Enemies: Spells like faerie fire (imposes disadvantage) effectively increase your AC by 5 against that target.
4. Mobility: High Dex characters can use hit-and-run tactics to avoid multiple attacks.
5. Minion Tactics: Use summons or allies to draw fire away from you.
6. Armor Swapping: Carry different armor types for different situations (e.g., stealth vs. combat).
7. Temporary Buffs: Use spells like shield of faith (+2 AC) or barkskin (AC 16) when expecting tough fights.

AC and Character Builds

Different character concepts prioritize AC differently:

• Tanks (Paladins, Fighters): Aim for AC 20+ through heavy armor, shields, and magic items.
• Skirmishers (Rogues, Rangers): Focus on medium armor with high Dex for AC 17-19.
• Spellcasters (Wizards, Sorcerers): Often rely on mage armor (AC 13-15) plus shields.
• Hybrids (Clerics, Druids): Balance armor with spellcasting needs (e.g., medium armor for clerics).
• Unarmored Builds (Monks, Barbarians): Invest in Dex/Wis/Con for AC 16-18 without armor.

Your character’s role in the party should inform your AC optimization strategy.

AC in PvP Combat

Player vs. Player combat puts special emphasis on AC:

• Attack Bonuses: Player characters often have higher attack bonuses than monsters, making high AC even more valuable.
• Critical Hits: The 5% chance on a 20 makes high AC particularly important against player attackers.
• Save-or-Suck Spells: Many PvP builds focus on saves rather than attack rolls, reducing AC’s importance.
• Action Economy: The Dodge action becomes more valuable in PvP where every attack counts.
• Magic Items: PvP often assumes higher magic item availability, enabling AC 22+ builds.

In organized play like Adventurers League, AC optimization becomes a key part of PvP preparation.

Future of AC in D&D

As D&D evolves, we may see changes to the AC system:

• More Dynamic AC: Systems where AC changes based on actions taken (e.g., lower AC after attacking).
• Location-Based Hits: More granular hit location systems that interact with armor types.
• Armor as DR: Potential shift toward damage reduction rather than to-hit modification.
• Class-Specific AC: More unique AC calculation methods for different classes.
• Environmental AC: More interaction between armor and environmental effects (heat, cold, etc.).

The D&D Studio website sometimes previews upcoming mechanics that might affect how AC works in future editions.

Authoritative Resources on Armor

For additional research on historical armor and its representation in gaming:

• Metropolitan Museum of Art – Arms and Armor Collection: Extensive collection of historical armor with detailed descriptions.
• Royal Armouries Museum: One of the world’s leading collections of arms and armor with educational resources.
• Armor and Arms Historical Research: Academic resources on historical combat and armor effectiveness.