5e Armor Class Calculation Guide & Calculator

Understanding how Armor Class (AC) is calculated in Dungeons & Dragons 5th Edition is crucial for both players and Dungeon Masters. It determines how difficult it is for an attack to hit a creature, directly impacting survivability and combat strategy. This guide breaks down the core rules for AC and provides a handy calculator to quickly determine your character's defense.

The Fundamentals of Armor Class (AC)

Armor Class (AC) represents how well a character or creature can avoid being wounded in combat. When an attack roll is made against a target, the attacker must roll a number equal to or greater than the target's AC to hit. A higher AC means a character is harder to hit, making them more resilient in battle.

The Basic Formula: 10 + Dexterity Modifier

For any creature not wearing armor, its AC is a base of 10 plus its Dexterity modifier. This is the default for most monsters, NPCs, and player characters who choose not to wear armor, or are proficient with none.

• Example: A wizard with a Dexterity of 14 (+2 modifier) has an AC of 10 + 2 = 12 when unarmored.

Armor Types and Their Specifics

The type of armor a character wears significantly alters their AC calculation. Proficiency in an armor type is required to wear it effectively; otherwise, you suffer disadvantages like disadvantage on ability checks, saving throws, and attack rolls that involve Strength or Dexterity, and you can't cast spells.

Light Armor

Light armor is made from supple and thin materials, allowing the wearer to move freely. It adds your full Dexterity modifier to its base AC.

• Formula: Base AC of Armor + Dexterity Modifier
• Examples:
  • Leather Armor: 11 + Dex Modifier
  • Studded Leather Armor: 12 + Dex Modifier

Medium Armor

Medium armor offers more protection than light armor but restricts movement more. It adds your Dexterity modifier to its base AC, but only up to a maximum of +2.

• Formula: Base AC of Armor + Dexterity Modifier (max +2)
• Examples:
  • Hide Armor: 12 + Dex Modifier (max +2)
  • Chain Shirt: 13 + Dex Modifier (max +2)
  • Scale Mail: 14 + Dex Modifier (max +2)
  • Breastplate: 14 + Dex Modifier (max +2)
  • Half Plate Armor: 15 + Dex Modifier (max +2)
• Important: If your Dexterity modifier is +3 or higher, you still only add +2 to your AC when wearing medium armor.

Heavy Armor

Heavy armor provides the best protection but is cumbersome and requires great strength. It does not add your Dexterity modifier to its base AC at all.

• Formula: Base AC of Armor (no Dex Modifier)
• Examples:
  • Ring Mail: 14 AC
  • Chain Mail: 16 AC
  • Splint Armor: 17 AC
  • Plate Armor: 18 AC
• Strength Requirement: Most heavy armors have a Strength score requirement. If you wear heavy armor without meeting this requirement, your speed is reduced by 10 feet.

Shields

A shield provides a flat bonus to your AC. You must be proficient with shields to gain this benefit.

• Bonus: +2 AC
• Stacking: A shield's bonus stacks with any type of armor or Unarmored Defense (Barbarian). Monks, however, cannot benefit from a shield while using their Unarmored Defense feature.

Special Unarmored Defenses

Some classes have unique ways to calculate AC when not wearing armor, often incorporating other ability modifiers.

Barbarian's Unarmored Defense

If you are not wearing any armor, your AC is 10 + your Dexterity modifier + your Constitution modifier. You can still use a shield and gain its benefit.

• Formula: 10 + Dexterity Modifier + Constitution Modifier
• Example: A Barbarian with Dex 14 (+2) and Con 16 (+3) has an AC of 10 + 2 + 3 = 15. If they also use a shield, their AC would be 17.

Monk's Unarmored Defense

While you are not wearing any armor and not wielding a shield, your AC is 10 + your Dexterity modifier + your Wisdom modifier.

• Formula: 10 + Dexterity Modifier + Wisdom Modifier
• Example: A Monk with Dex 16 (+3) and Wis 16 (+3) has an AC of 10 + 3 + 3 = 16. Note that Monks typically cannot benefit from shields while using this feature.

Draconic Resilience (Sorcerer)

Some Draconic Bloodline Sorcerers gain an AC of 13 + their Dexterity modifier when not wearing armor. This cannot be combined with a shield.

• Formula: 13 + Dexterity Modifier

Other AC Modifiers and Considerations

Beyond armor and ability scores, several other factors can influence a character's AC:

• Magical Armor/Shields: Magic items like a +1 Shield or +2 Plate Armor directly increase the AC they provide.
• Spells: Spells such as Shield of Faith (+2 AC) or Barkskin (sets AC to 16, ignoring Dex mod) can temporarily alter AC.
• Cover: Being behind cover grants bonus AC. Half cover (+2 AC), three-quarters cover (+5 AC), and total cover (cannot be targeted directly).
• Feats: Some feats, like the Defensive Duelist feat, can temporarily boost AC.
• Class Features: Features like the Fighter's Fighting Style (Defense) grant a permanent +1 AC while wearing armor.

How to Use the 5e AC Calculator

Our calculator simplifies the process:

1. Select your primary defense method: Choose whether you're relying on armor, or one of the unarmored defense options.
2. Fill in the relevant details: Depending on your choice, input your armor's base AC, Dexterity, Wisdom, or Constitution modifiers.
3. Check the 'Has Shield' box if you are using one and it's applicable to your defense method (i.e., not a Monk's Unarmored Defense).
4. Add any 'Other Modifiers' from magic items, spells, or temporary effects.
5. Click 'Calculate AC' to see your total Armor Class!

Mastering AC calculation is a small but vital step in becoming a D&D expert. Use this guide and calculator to ensure your characters are always prepared for battle!