D&D 5e Armor Class Calculator

Common base formulas

Unarmored = 10 + Dexterity modifier

Light armor = armor base + full Dexterity modifier

Medium armor = armor base + capped Dexterity modifier

Heavy armor = fixed armor base

Barbarian = 10 + Dexterity + Constitution

Monk = 10 + Dexterity + Wisdom

Mage Armor = 13 + Dexterity

Calculation order

First, choose one legal base formula. Second, apply shield, armor enhancement, class features, magic items, spells, and cover. Third, apply a minimum AC effect when the calculated value is lower. Finally, a manual override replaces every other result when enabled.

The calculator keeps base formulas separate. It never adds Barbarian, Monk, Mage Armor, natural armor, and manufactured armor formulas together.

Start with one defensive foundation

Armor Class represents how difficult a creature is to hit with an attack roll. A higher number usually means attacks need a better d20 result. The most important calculation rule is that a character normally uses one base AC formula. Wearing armor supplies one formula. Remaining unarmored supplies another. Class abilities, natural armor, and protective spells may offer alternatives, but those alternatives are compared rather than combined.

Automatic mode checks the valid formulas and selects the highest result. Manual mode is useful when a player deliberately chooses a lower formula, follows a campaign ruling, or wants to inspect a specific class feature. Invalid choices create explanations instead of silently producing an impossible total.

Understand Dexterity limits

Light armor generally adds the full Dexterity modifier. Medium armor normally limits the positive Dexterity contribution. Heavy armor ignores Dexterity entirely. Negative modifiers can matter differently depending on the selected equipment and campaign interpretation, so custom mode remains available. Medium Armor Master can raise the configured cap, while heavy armor may carry a Strength requirement and a Stealth drawback.

Add only compatible bonuses

After choosing the base, the calculator adds compatible bonuses. A shield can add its normal bonus and a separate magical enhancement. Defense Fighting Style requires worn armor. Bracers of Defense require no armor and no shield. Bladesong has equipment restrictions. The calculator records every ignored bonus, helping players discover why an expected number did not appear.

Temporary effects deserve special attention. The Shield spell is a short defensive reaction. Cover depends on the attacker’s position. Haste and Shield of Faith may require concentration. Barkskin behaves as a minimum in the supplied presets, not a simple additive bonus. Keeping these effects separate makes a character sheet easier to use during combat.

Compare defense with attack probability

An AC number becomes more useful when paired with an enemy attack bonus. The hit analysis checks every natural d20 result and supports normal rolls, advantage, disadvantage, and a highest-of-three mode. It reports hit probability, critical probability, expected hits, and the chance that at least one attack lands. These values help a game master evaluate encounters without treating Armor Class as the character’s only defense.