Armor Class Calculator

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Reviewed by David Chen, TTRPG Rules Consultant

This calculator ensures adherence to standard role-playing game core rules for accurate Armor Class determination.

The **Armor Class Calculator** is an essential tool for players and game masters in tabletop role-playing games, allowing for the quick and accurate determination of a character’s defensive rating against physical attacks.

Armor Class Calculator

Your Calculated Armor Class (AC) is:

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Calculation Breakdown:

Enter your values and click Calculate AC to see the detailed steps.

Armor Class Calculator Formula

Total AC = Base AC + Dexterity Modifier + Armor Bonus + Shield Bonus + Miscellaneous Modifiers

Formula Source: Roll20 Compendium (Armor Class) | Wizards of the Coast Rules

Variables Explained

Understanding the components that contribute to your character’s Armor Class is crucial:

  • Base AC (10): The default AC for a character wearing no armor. Some class features or conditions can alter this base value.
  • Dexterity Modifier: The bonus (or penalty) derived from your character’s Dexterity score. This is often capped by the type of armor worn (e.g., heavy armor usually has a cap of 0 or +1).
  • Armor Base/Bonus: The numerical defense provided by the specific armor worn (e.g., Studded Leather: 12 + Dex Mod; Plate: 18). Enter the fixed armor AC or the base bonus here.
  • Shield Bonus: Typically a +2 bonus granted by equipping a shield.
  • Miscellaneous Modifiers: Any other bonuses, such as from magical items (e.g., Ring of Protection +1), spells, or class abilities (e.g., the Defense fighting style).

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What is Armor Class (AC)?

Armor Class (AC) is the measurement of how difficult a character or monster is to hit with an attack. In most tabletop systems, when a character is targeted by an attack, the attacker rolls a twenty-sided die (d20), adds their attack modifier, and compares the result to the target’s AC. If the result equals or exceeds the AC, the attack hits.

A higher AC means the character is better defended, either through physical armor, the quickness of their reflexes (Dexterity), magical protection, or a combination of all three. Correctly calculating AC is vital for maintaining game balance and accurately resolving combat encounters.

The total AC is not just the value of the armor itself; it’s a dynamic number reflecting the character’s entire defensive posture, including ability scores and special features.

How to Calculate Armor Class (Example)

Let’s walk through an example for a heavily armored Paladin:

  1. Start with Base AC: The character is wearing **Plate Armor**, which has a fixed AC of 18 (so Base AC = 18, and the initial 10 is replaced).
  2. Add Dexterity Modifier: Plate Armor is Heavy Armor, so the Dexterity Modifier does not apply (Dex Mod = 0).
  3. Add Shield Bonus: The character is wielding a **Shield**, providing a +2 bonus (Shield Bonus = 2).
  4. Apply Miscellaneous Modifiers: The Paladin has the **Defense Fighting Style** (+1) and a **Cloak of Protection** (+1), totaling +2 (Misc Mod = 2).
  5. Calculate Total AC: $$AC = 18 (Armor) + 0 (Dex) + 2 (Shield) + 2 (Misc) = 22$$
  6. The Paladin’s final Armor Class is 22, making them exceptionally difficult to hit.

Frequently Asked Questions (FAQ)

What is the maximum Dexterity Modifier I can add to AC?

It depends entirely on the type of armor. Heavy armor typically adds 0. Medium armor often caps the bonus at +2. Light armor allows the full Dexterity Modifier to be added. If you are wearing no armor, you can add the full modifier (often combined with a base AC of 10 or 12).

Do I add my Armor Bonus to my Base AC of 10?

No, usually the Armor Base (e.g., 18 for Plate Armor, 14 for Breastplate) replaces the default 10 AC, but this varies by specific ruleset. For this calculator, you should enter the primary defensive value (the armor’s AC or 10 if unarmored) in the ‘Armor Base/Bonus’ field.

Can Armor Class be negative?

In some older editions of TTRPGs, AC could be negative, but in modern systems like D&D 5th Edition, AC is a positive integer, usually starting at 10. Penalties (like a negative Dexterity modifier) will reduce AC but rarely below the default 10.

Does my Constitution Modifier affect AC?

Not directly for most classes. However, certain Barbarian and Monk class features allow you to substitute or add your Constitution or Wisdom modifier, respectively, to your AC when you are not wearing armor.

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