How to Calculate Armor Class Calculator
Determine your character's protection level based on dexterity, armor type, and defensive bonuses.
Choose the primary protection your character is wearing.
Enter your full Dexterity score (e.g., 14, 16). The modifier is calculated automatically.
Add bonuses from spells (Shield of Faith), magic armor (+1, +2), or class features.
Formula: Base 10 + Dexterity (+0)
AC Composition Visualized
Blue: Base Armor | Green: Dexterity | Orange: Shields & Magic
| Armor Category | Base AC | Dexterity Modifier Impact | Stealth Impact |
|---|---|---|---|
| Unarmored | 10 | Full Modifier | No Disadvantage |
| Light | 11 – 12 | Full Modifier | Varies |
| Medium | 12 – 15 | Max +2 | Varies |
| Heavy | 14 – 18 | No Impact | Disadvantage |
What is Armor Class?
How to calculate armor class is one of the most fundamental questions for any tabletop role-playing game enthusiast. Armor Class, or AC, represents how difficult it is for a creature to land a damaging blow on you. It isn't just about the thickness of your plate mail; it encompasses your physical agility, your equipment, and any magical protections you might have active.
Who should use it? Players building new characters, dungeon masters tracking NPCs, and strategists trying to optimize their survivability in combat. A common misconception is that a high Armor Class means you are "invincible." In reality, AC only protects against physical attacks that require an attack roll—it does not protect you from spells that require saving throws, like Fireball.
Armor Class Formula and Mathematical Explanation
The core logic of how to calculate armor class depends entirely on the type of armor being worn. The math follows a specific priority: your base armor value plus your effective Dexterity modifier, plus any external bonuses.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Base AC | Fixed value provided by the armor type | Integer | 10 to 18 |
| Dex Mod | (Dexterity Score – 10) / 2 | Modifier | -5 to +10 |
| Shield | Bonus for carrying a shield | Modifier | +2 |
| Misc | Magic items, spells, and class features | Modifier | 0 to +5 |
Step-by-step derivation:
1. Determine your Armor Class base from your armor (e.g., Plate is 18).
2. Calculate your Dexterity modifier.
3. Apply the Dexterity cap (Heavy: 0, Medium: 2, Light: No Cap).
4. Sum the Base, Applied Dex, Shield, and Magic bonuses.
Practical Examples (Real-World Use Cases)
Example 1: The Nimble Rogue
Inputs: Studded Leather (Base 12), Dexterity 18 (+4 modifier).
Calculation: 12 (Base) + 4 (Dex) = 16 AC.
Result: The rogue relies on agility to boost their Armor Class.
Example 2: The Heavily Armored Fighter
Inputs: Plate Armor (Base 18), Shield (+2), Dexterity 10 (+0 modifier).
Calculation: 18 (Base) + 0 (Dex) + 2 (Shield) = 20 AC.
Result: Despite low agility, the fighter achieves a massive Armor Class through heavy gear.
How to Use This Armor Class Calculator
Follow these steps to ensure you are accurately understanding how to calculate armor class:
- Step 1: Select your Armor Type from the dropdown menu. This sets your base AC.
- Step 2: Enter your full Dexterity Score. The tool will automatically calculate the modifier.
- Step 3: Toggle the shield option if you are wielding one.
- Step 4: Add any miscellaneous bonuses from magic items like a Cloak of Protection.
- Interpretation: The final large number is what an enemy must meet or beat with their attack roll to hit you.
Key Factors That Affect Armor Class Results
Understanding how to calculate armor class requires looking at several dynamic factors:
- Armor Proficiency: If you wear armor you aren't proficient in, you have disadvantage on several checks and cannot cast spells.
- Dexterity Caps: Medium armor limits your bonus to +2, while Heavy armor ignores it entirely. This is crucial for high-Dexterity builds.
- Natural Armor: Some races (like Lizardfolk) have a natural base Armor Class that overrides the standard "10 + Dex" unarmored rule.
- Magic Items: Rings of Protection or +1 Armor directly increase the total sum.
- Cover: Half-cover provides a +2 bonus, and three-quarters cover provides a +5 bonus to your Armor Class during combat.
- Spells: Temporary buffs like Mage Armor (changes base to 13) or Shield (adds +5 reaction bonus) fluctuate your AC mid-fight.
Frequently Asked Questions (FAQ)
Does Mage Armor stack with physical armor?
No. Mage Armor sets your base AC to 13 + Dex. If you put on physical armor, you must choose which formula to use; they do not stack.
Can my Armor Class be lower than 10?
Yes. If you are unarmored and have a Dexterity score below 10, your negative modifier reduces your Armor Class below 10.
Do shields count as armor?
Shields provide a bonus to your Armor Class but are distinct from the "armor" you wear on your body for proficiency purposes.
What is the highest possible AC?
While theoretical, with plate +3, a shield +3, and various spells, an Armor Class can exceed 30.
How does Barbarian Unarmored Defense work?
It changes the formula to 10 + Dex Mod + Con Mod. This is a separate way to calculate armor class.
Does Dexterity affect Plate Armor?
No, Heavy armor like Plate ignores your Dexterity modifier entirely, whether it is positive or negative.
Is Armor Class used for saving throws?
No, Armor Class only applies to attack rolls directed at you.
Does a shield hinder my spellcasting?
Only if you are not proficient with shields or if the spell requires a somatic component and your hands are full.
Related Tools and Internal Resources
- Ability Score Guide: Learn how Dexterity impacts more than just your Armor Class.
- Spellcasting Basics: How spells like Shield of Faith can alter how you calculate armor class.
- Combat Maneuvers: Strategies for bypassing a high Armor Class.
- Equipment List: Prices and weights for all items mentioned in this Armor Class guide.
- Character Builder: A tool to automate how to calculate armor class for your hero.
- DM Screen Tools: Quick references for Armor Class values of common monsters.