How Do You Calculate Your Armor Class

Use this premium D&D 5e armor class calculator to estimate AC from armor, Dexterity, shield use, class-based unarmored defense, natural armor, cover, and miscellaneous bonuses.

Your Armor Class Result

See your final AC, a rules-style breakdown, and a quick view of how each component contributes to defense.

Calculator assumes standard 5e-style armor class rules. Specific class features, magic items, and house rules can change the final number.

Expert Guide: How Do You Calculate Your Armor Class?

Armor Class, usually shortened to AC, is one of the most important defensive statistics in tabletop fantasy roleplaying. If you have ever asked, “how do you calculate your armor class,” the short answer is that you begin with a base formula and then apply the correct armor rule, your relevant ability modifier, and any legal bonuses such as a shield, cover, class features, spells, natural armor, or magic effects. The exact formula depends on what kind of protection your character is using.

In the most common 5e-style rules framework, AC represents how hard you are to hit with an attack roll. When an attacker rolls a d20, adds their attack bonus, and meets or beats your AC, the attack hits. If the total is lower than your AC, the attack misses. That makes AC a direct gatekeeper between incoming attacks and your hit points. Small AC differences matter a lot because every +1 changes the number an attacker needs on the die.

• Base AC formulas
• Light armor rules
• Medium armor caps
• Heavy armor interaction
• Shield and cover
• Unarmored defense

The basic formula behind Armor Class

For many characters, the most familiar starting point is 10 + Dexterity modifier. If a character wears no armor and has no feature that changes the formula, this is often their default AC. A character with a Dexterity modifier of +3 would therefore have an AC of 13 before any extra bonuses are applied.

However, armor can replace or modify that base formula:

• Light armor adds a fixed armor value and lets you apply your full Dexterity modifier.
• Medium armor adds a fixed armor value but caps the Dexterity contribution, usually at +2.
• Heavy armor gives a fixed AC value and normally ignores Dexterity for AC entirely.
• Special features like Barbarian Unarmored Defense or Monk Unarmored Defense use unique formulas.
• Spells and traits such as Mage Armor or natural armor may create alternate calculations.

Important rule concept: when multiple AC calculations are available, you normally choose the one formula that applies. Then you add bonuses that explicitly stack, such as a shield or cover, if the rules allow them.

How to calculate AC step by step

1. Determine your base AC formula. Are you unarmored, wearing armor, using Mage Armor, or benefiting from a class feature?
2. Add the correct ability modifier. Usually this is Dexterity, but some features also use Constitution or Wisdom.
3. Apply any caps. Medium armor generally limits Dexterity added to AC to +2.
4. Add shield bonus if legal. A standard shield is usually +2 AC.
5. Add natural armor or miscellaneous bonuses if the rules say they stack.
6. Add situational cover. Half cover is often +2 AC, while three-quarters cover is often +5 AC.
7. Verify restrictions. Some class features do not work while you wear armor or wield a shield.

This process sounds simple, but the most common mistakes happen when players accidentally stack two different base formulas, forget a Dexterity cap on medium armor, or add Dexterity to heavy armor when they should not.

Armor formulas by category

Below is a practical comparison of standard armor values commonly used in 5e-style play. These values are game statistics that players regularly use to calculate legal AC totals at the table.

Armor Type	Item	Base AC Formula	Dexterity Applied?	Typical Notes
Unarmored	No armor	10 + Dex	Full	Default for many characters
Light	Padded / Leather	11 + Dex	Full	Good for agile builds
Light	Studded Leather	12 + Dex	Full	Best common light armor AC
Medium	Hide	12 + Dex max 2	Capped at +2	Useful if Dex is moderate
Medium	Chain Shirt	13 + Dex max 2	Capped at +2	Solid all-around option
Medium	Scale Mail / Breastplate	14 + Dex max 2	Capped at +2	High AC without heavy armor
Medium	Half Plate	15 + Dex max 2	Capped at +2	Top standard medium armor AC
Heavy	Ring Mail	14	No	Dex does not change AC
Heavy	Chain Mail	16	No	Strong fixed defense
Heavy	Splint	17	No	Very high AC
Heavy	Plate	18	No	Highest standard armor AC

That table also shows why Dexterity matters differently depending on armor type. A rogue with a +4 Dexterity modifier in studded leather gets 16 AC before shield or magic. A fighter with chain mail starts at 16 AC even with low Dexterity. A character in half plate with +4 Dexterity still gains only +2 from Dexterity, because medium armor caps that bonus.

Unarmored defense and special formulas

Some characters calculate AC without wearing traditional armor at all. Two of the most well-known class features are:

• Barbarian Unarmored Defense: 10 + Dexterity modifier + Constitution modifier
• Monk Unarmored Defense: 10 + Dexterity modifier + Wisdom modifier

These are not bonuses added onto another armor formula. They are alternate ways to calculate AC. For example, a Barbarian with Dex +2 and Con +3 would have AC 15 before shield use or magic. A Monk with Dex +3 and Wis +4 would have AC 17 before other effects. Because these formulas can become very strong, they are often central to class optimization.

Spells can also alter the formula. Mage Armor typically sets AC to 13 + Dexterity modifier, which is usually excellent for characters who cannot or do not wear armor. Similarly, some species or monsters have natural armor, such as 13 + Dexterity modifier, which functions as its own AC calculation rather than as a generic stacking bonus.

Shields, cover, and stacking rules

A standard shield usually grants +2 AC. This is one of the cleanest and most reliable defensive boosts in the game. If your chosen armor calculation allows shield use, it can significantly improve survivability. For example, chain mail plus shield commonly becomes 18 AC, while plate plus shield reaches 20 AC before magic.

Cover is also important, especially in tactical encounters:

• Half cover: often +2 AC
• Three-quarters cover: often +5 AC

Cover can transform combat outcomes. A character with a normal AC of 16 behind three-quarters cover effectively defends at AC 21 against qualifying attacks. That often forces enemies to rely on very high attack bonuses or lucky rolls.

What usually does not stack is two different base AC formulas. You do not generally combine Mage Armor with studded leather, and you do not add Barbarian Unarmored Defense on top of heavy armor. Choose the valid formula, then add any extra bonuses that explicitly apply.

Why one point of AC matters: hit probability examples

Players sometimes underestimate AC because it looks like a small number compared with hit points or damage output. In reality, every point can produce a measurable change in expected survival. If an attacker has a +5 attack bonus, then the AC you choose directly changes the d20 result needed to hit. The table below uses standard attack math, where a natural 1 misses and a natural 20 hits.

Target AC	Minimum Roll Needed vs +5 Attack	Approximate Hit Chance	Approximate Miss Chance
12	7	70%	30%
14	9	60%	40%
16	11	50%	50%
18	13	40%	60%
20	15	30%	70%
22	17	20%	80%

That means raising AC from 16 to 18 against a +5 attack reduces incoming hit probability by about 10 percentage points. Over many attack rolls, that is a major durability increase. This is one reason shields, cover, and strong armor choices are so valuable.

Common examples of AC calculation

Example 1: Rogue in studded leather
A rogue wears studded leather and has Dexterity +4. Studded leather is 12 + Dex, so the final AC is 16.

Example 2: Cleric in half plate with shield
Half plate is 15 + Dex max 2. If the cleric has Dexterity +1 and uses a shield, AC is 15 + 1 + 2 = 18.

Example 3: Fighter in plate with shield
Plate gives a fixed AC of 18, and Dexterity does not apply. Add a shield for +2, making total AC 20.

Example 4: Monk with high Wisdom
A monk with Dex +3 and Wis +4 uses Unarmored Defense: 10 + 3 + 4 = 17 AC.

Example 5: Sorcerer using Mage Armor
If a sorcerer has Dex +2, Mage Armor sets AC to 13 + 2 = 15.

Optimization tips for better AC

• Use light armor if your Dexterity is high and you want stealth-friendly defense.
• Use medium armor if your Dexterity is moderate and you want a strong base AC without needing very high Dex.
• Use heavy armor if your build prioritizes Strength and reliable fixed AC.
• Carry a shield whenever your class and playstyle permit it.
• Seek cover in ranged fights. It is one of the easiest situational AC boosts.
• Know when a special formula like Mage Armor or Unarmored Defense outperforms mundane armor.
• Remember that AC is only one defense layer. Saving throws, resistances, temporary hit points, and battlefield control all matter too.

Mistakes players make when calculating Armor Class

1. Adding Dexterity to heavy armor. Heavy armor normally ignores Dexterity for AC.
2. Forgetting the medium armor cap. A +4 Dexterity modifier does not become +4 AC in half plate; it stays capped at +2.
3. Stacking two AC formulas. You usually choose one legal formula rather than combining multiple base calculations.
4. Ignoring shield restrictions. Some class features work only when specific gear conditions are met.
5. Overlooking cover. Temporary battlefield AC bonuses are often decisive in ranged combat.

Useful authority links for the math behind attack odds and statistics

Armor Class is part rules knowledge and part probability. If you want to understand why changing AC by one or two points matters so much, these statistics resources are helpful for attack-roll math and probability thinking:

• U.S. Census Bureau: What Is Probability?
• Penn State University: Probability Theory
• University-linked educational probability primer resources often echo these same core principles

Although those sources are not game-rule pages, they are directly relevant to understanding hit chance, expected outcomes, and why AC optimization changes survival over repeated attack rolls.

Final takeaway

If you want the fastest answer to “how do you calculate your armor class,” use this rule of thumb: start with the correct AC formula for your armor or feature, add the allowed ability modifier, then add legal bonuses like a shield, cover, or miscellaneous effects. Light armor uses full Dexterity, medium armor usually caps Dexterity at +2, and heavy armor normally ignores Dexterity. Unarmored characters may rely on 10 + Dex or on alternate class formulas such as 10 + Dex + Con or 10 + Dex + Wis.

The calculator above lets you test different setups quickly, compare the impact of armor choices, and see how AC influences enemy hit chance. If you are building a durable front-liner, a skirmishing rogue, or a spellcaster deciding between Mage Armor and mundane gear, understanding AC is one of the best ways to make your character tougher and more efficient.