Understanding Armor Class (AC) in D&D 5e
In Dungeons & Dragons 5th Edition, your Armor Class (AC) determines how difficult it is for enemies to successfully land an attack on your character. Whether you're building a heavily armored Fighter or an agile Monk relying on Unarmored Defense, calculating your total AC correctly is one of the most critical steps in character creation and combat preparation.
Use the interactive calculator above to quickly find your final AC by selecting your class features, armor type, and any active spell buffs.
Core Formula: Base AC vs. Bonus AC
The most common mistake new D&D 5e players make is trying to stack multiple Base AC formulas. The fundamental rule of D&D 5e Armor Class is: You can only ever benefit from one Base AC formula at a time.
However, once you have established your Base AC, you can add any number of Bonus AC modifiers (such as shields and magic rings), provided you meet their requirements.
D&D 5e Armor Class Base Formulas
Depending on your equipment or class features, your Base AC will follow one of these distinct calculations:
| Base Source | Formula | Special Requirements |
|---|---|---|
| Unarmored | 10 + DEX Modifier | None |
| Light Armor | Armor Base + DEX Modifier | Must be wearing Light Armor |
| Medium Armor | Armor Base + Min(DEX Modifier, 2) | Maximum +2 from DEX |
| Heavy Armor | Armor Base | Ignores DEX completely |
| Barbarian Unarmored | 10 + DEX + CON | Cannot wear armor; shield allowed |
| Monk Unarmored | 10 + DEX + WIS | Cannot wear armor; NO shield allowed |
| Mage Armor (Spell) | 13 + DEX Modifier | Cannot wear armor |
| Draconic Resilience | 13 + DEX Modifier | Cannot wear armor (Sorcerer Subclass) |
Step-by-Step AC Calculation Example
Let's look at a realistic combat scenario for a Level 3 Barbarian facing off against a horde of goblins.
Character Stats:
Dexterity: 14 (+2 Modifier)
Constitution: 16 (+3 Modifier)
Equipment: A Wooden Shield (+2 AC) and no armor.
Buffs: An allied Cleric casts Shield of Faith (+2 AC).
Step 1: Choose the Base Formula
Because this character is a Barbarian, they can use the Barbarian Unarmored Defense feature. According to the official D&D Basic Rules, this formula is 10 + DEX + CON.
Base AC = 10 + 2 (DEX) + 3 (CON) = 15.
Step 2: Add Applicable Bonuses
Shield Bonus: +2 AC
Shield of Faith Spell: +2 AC
Step 3: Calculate Final AC Final AC = 15 + 2 + 2 = 19.
Common Pitfalls and Restrictions
Monks and Shields Do Not Mix Unlike Barbarians, Monks lose their Unarmored Defense entirely if they equip a shield. If a Monk with 16 DEX and 16 WIS equips a shield, their AC drops from 16 (10+3+3) to 15 (10+3 for base unarmored, +2 for shield).
Negative Dexterity Modifiers If your Dexterity modifier is negative (e.g., -1), it will reduce your AC if you are unarmored, wearing Light Armor, or wearing Medium Armor. The only way to ignore a negative Dexterity modifier is by wearing Heavy Armor.