armor class dnd calculator

How Armor Class Works in D&D

Armor Class (AC) is the number enemies must meet or beat on an attack roll to hit your character. It is one of the most important defensive stats in Dungeons & Dragons because it determines how often weapon attacks and many spell attacks land.

In most games, your AC comes from one of these sources:

• Armor (light, medium, or heavy)
• Dexterity modifier (fully, partially capped, or not used)
• Class features like Unarmored Defense
• Shield (+2 in most cases)
• Bonuses from magic items, spells, fighting styles, and cover

AC Formulas by Armor Type

Light Armor

Light armor always adds your full Dexterity modifier. Great for high-Dex classes like rogues, rangers, and dexterity-based fighters.

• Padded/Leather: 11 + Dex mod
• Studded Leather: 12 + Dex mod

Medium Armor

Medium armor adds Dexterity modifier up to a maximum of +2. This rewards moderate Dex but not extreme investment.

• Hide: 12 + Dex mod (max +2)
• Chain Shirt: 13 + Dex mod (max +2)
• Scale Mail/Breastplate: 14 + Dex mod (max +2)
• Half Plate: 15 + Dex mod (max +2)

Heavy Armor

Heavy armor ignores Dexterity modifier completely. You get a fixed AC value and can focus your ability scores elsewhere.

• Ring Mail: 14
• Chain Mail: 16
• Splint: 17
• Plate: 18

Unarmored and Special Defenses

• No armor: 10 + Dex mod
• Mage Armor: 13 + Dex mod
• Barbarian Unarmored Defense: 10 + Dex mod + Con mod
• Monk Unarmored Defense: 10 + Dex mod + Wis mod
• Tortle natural armor: 17 base

Using the Calculator Effectively

Use this calculator as a quick planning tool for builds and equipment choices. It is especially useful when comparing:

• Dexterity-based builds vs. heavy armor builds
• Shield vs. two-handed weapon setups
• Class features (Monk/Barbarian) against standard armor options
• Magic item upgrades and temporary cover bonuses

If you are multiclassing, this tool can help identify your best defensive configuration at different levels.

Example AC Calculations

Example 1: Rogue in Studded Leather

A rogue with Dex 18 has a +4 modifier. Studded leather gives 12 + Dex mod, so AC is 16. Add a defensive magic item (+1), and total AC becomes 17.

Example 2: Fighter in Plate with Shield

Plate armor gives AC 18. Add shield (+2) for AC 20. If the fighter also has the Defense style (+1), AC becomes 21 before other bonuses.

Example 3: Barbarian with Unarmored Defense

Dex 16 (+3) and Con 16 (+3) gives 10 + 3 + 3 = AC 16. A shield can increase this to 18 in many builds.

Common Mistakes to Avoid

• Applying Dexterity to heavy armor. Heavy armor uses fixed AC values.
• Ignoring medium armor cap. Medium armor maxes Dex bonus at +2.
• Stacking incompatible formulas. You generally choose one AC formula at a time.
• Forgetting temporary effects. Cover and spells can dramatically change survivability.

Final Tips for Better Survivability

AC is powerful, but it is only one layer of defense. Strong characters combine AC with smart positioning, hit points, resistances, reactions, and party support. Use this calculator to optimize your baseline, then pair it with tactical play at the table.

Bookmark this page when planning new characters, evaluating loot, or deciding if a feat, fighting style, or item upgrade is worth it for your next level.