How to Calculate Armor Class in 5e D&D
Many factors can go into Armor Class. It can be incredibly complicated for some characters, incorporating class, race, and other features on top of your type of armor. For others, it can be as simple as 10 + Dex modifier.
Armor Class is important in combat because it determines whether you succeed or fail in protecting yourself. This guide provides a comprehensive understanding of Armor Class. It covers Armor Class basics, the impact items, enhancements, and other bonuses.
What is AC?
Armor class, or AC, is a character’s ability to block or dodge an attack. When you or the enemy make an attack roll, you check AC to determine if it hits. If the attack roll is less than the AC, the attack misses. If the attack roll is equal to or greater than the AC, the attack hits.
Some attacks, like high-level spells, don’t check AC and instead have the target make a saving throw. A high AC doesn’t guarantee protection in all situations. Armor that gives a high AC can make it harder to pass Dexterity saving throws. You may feel indestructible in full plate armor, but one unexpected Fireball can burn you to a crisp.
AC for NPCs
While I’ll mostly focus on AC from the player’s perspective, it’s always important to note that these can also apply to Nonplayer Characters (NPCs) you make as a DM. For enemy NPCs and monsters, refer to its stat block for AC. For regular NPCs, an AC of 12 is reasonable.
DM Tip: Armor class isn’t only for living things; objects also have AC! Paper has an AC of 11, while adamantine has an AC of 23. Check out the details here.
You can also adjust AC to the enemy’s challenge rating. CR 1 enemies have an AC of around 13, while CR 20 enemies have an AC of around 19. You may adjust the AC based on the armor the enemy is wearing or other AC Bonuses they might have.
Using Armor
Everyone can wear armor to increase their AC, but not everyone can maximize its effectiveness. Your class determines your Proficiency in different types of armor and shields. Here’s a breakdown of armor proficiencies by class:
| Class | Armor Proficiencies |
| Artificer | Light armor, Medium armor, shields |
| Barbarian | Light armor, medium armor, shields |
| Bard | Light armor |
| Cleric | Light armor, medium armor, shields |
| Druid | Light armor, medium armor, shields |
| Fighter | All armor, shields |
| Monk | None |
| Paladin | All armor, shields |
| Ranger | Light armor, medium armor, shields |
| Rogue | Light armor |
| Sorcerer | None |
| Warlock | Light armor |
| Wizard | None |
Wearing armor that your character isn’t proficient in will give you a penalty on Strength or Dexterity checks. You can’t cast spells wearing armor or wielding a shield if you aren’t proficient!
Types of Armor
Armor has three main categories: light, medium, and heavy. You can also use no armor. Depending on what type of armor you wear changes how you will calculate AC. Sorcerers often wear plain clothing, such as robes, while Paladins wear heavy armor.
Light Armor
Light armor is the most common type of armor. It is cheap, and 10 classes can use it without issue. Here is a list of the 3 types of light armor and no armor:
| Armor Type | Cost | AC Calculation | Stealth Checks | Weight |
| Cloth (no armor) | Varies | 10 + Dex modifier | — | <1 lb. |
| Padded | 5 gp | 11 + Dex modifier | Disadvantage | 8 lbs. |
| Leather | 10 gp | 11 + Dex modifier | — | 10 lbs. |
| Studded Leather | 25 gp | 12 + Dex modifier | — | 13 lbs. |
Wearing light armor is a great way to improve your character’s AC with minimal drawbacks, as long as you are proficient with it! Light armor also uses your Dexterity modifier to determine the final AC. Check out how Dexterity and other stats are determined here.
Medium Armor
Medium armor is when armor starts to get more complex. Here are the 5 types of medium armor:
| Armor Type | Cost | AC Calculation | Stealth Checks | Weight |
| Hide | 10 gp | 12 + Dex modifier (max 2) | — | 12 lbs. |
| Chain Shirt | 50 gp | 13 + Dex modifier (max 2) | — | 20 lbs. |
| Scale Mail | 50 gp | 14 + Dex modifier (max 2) | Disadvantage | 45 lbs. |
| Breastplate | 400 gp | 14 + Dex modifier (max 2) | — | 20 lbs. |
| Half Plate | 750 gp | 15 + Dex modifier (max 2) | Disadvantage | 40 lbs. |
Medium armor allows you to use your Dex mod when calculating your AC, but only up to +2. You must choose between price, protection, and stealthiness when picking medium armor.
Heavy armor
The highest level of armor is heavy armor, normally used by Fighters and Paladins. Heavy armor protects those who fight on the frontlines of battle. Here are the 4 types of heavy armor:
| Armor Type | Cost | AC Calculation | Strength required | Stealth Checks | Weight |
| Ring Mail | 30 gp | 14 | — | Disadvantage | 40 lbs. |
| Chain Mail | 75 gp | 16 | Str 13 | Disadvantage | 55 lbs. |
| Splint | 200 gp | 17 | Str 15 | Disadvantage | 60 lbs. |
| Plate | 1500 gp | 18 | Str 15 | Disadvantage | 65 lbs. |
Mundane heavy armor always has a disadvantage on Stealth checks, while only specific types of light and medium armor have this penalty. Some of the armor requires a minimum Strength Score, too! Heavy armor gives you a flat AC, so your dexterity modifier won’t affect your AC.
Shields
Shields are a sheet of metal or wood that you attach to your arm to help block attacks. This simple item gives you a +2 to your AC. Be careful, with a shield equipped, you won’t be able to do much with the hand that it’s in. Enchantment can improve the defenses of a shield up to +5!
Magic Armor
Magical enchantments can improve armor or give it special effects. Listing all magic armor would take too long, so go and explore what kinds of magic armor are available for yourself!
I mention two special metals that make armor magical: Adamantine and Mithral. It gains a special benefit if medium or heavy armor (excluding hide) is made with one of these metals.
Adamantine is the hardest substance in existence. Armor made with adamantine stops critical hits against you, turning them into normal hits.
Mithral is a light, flexible metal. Armor made from Mithral no longer causes a disadvantage on Stealth checks and has no Strength requirements to wear.
DM Tip: Putting on and taking off armor takes time. The time it takes depends on the type of armor. The Player’s Handbook calls it Donning (putting on) and Doffing (talking off) if you want to know the details. Most of the time, your players won’t be pressured to don or take off your armor.
Race Bonuses
Natural armor, like scales, shells, or exoskeletons, protects a creature. A Tortle’s shell is an extreme example. If you play a Tortle character, your base AC will be 17, but you won’t benefit from donning armor.
Lizardfolk have neutral armor with a base AC of 13 + Dex modifier. Lizardfolks won’t benefit from leather armor but may benefit from Plate armor. If you have more than one way to calculate your AC, always pick the highest one, as effects don’t normally stack
Class Bonuses
Some classes may have special bonuses to AC. Barbarians and Monks both have the level 1 feature of Unarmored Defence. If a Barbarian isn’t wearing armor, their base AC is 10 + Dex Mod + Constitution Mod. If a Monk isn’t wearing armor, their base AC is 10 + Dex Mod + Wisdom Mod.
Your Subclass may give you special armor effects. A Wizard Subclass, School of Invention, from this Unearthed Arcana has the feature Arcanomechanical Armor. It gives you proficiency in light armor and an enchanted suit of studded leather armor.
Look at your class features to find the special bonuses and modifiers you use for your AC.
Using Spells
Most spell casters will find that they have no armor proficiencies. These characters will be more vulnerable than their armored companions. Do not worry because there are ways to use magic to increase your AC.
Mage Armor is one common spell you can find in any cautious Sorcerer’s spell list. This first-level spell will give you an 8-hour boost to your AC. Here is the calculation for creatures wearing mage armor:
13 + Dexterity Modifier = AC
Mage Armor doesn’t stack with other armor effects. If you give mage armor to a creature with natural armor or Unarmoured defense, use whichever gives the highest AC.
Shield, another first-level spell, gives a +5 bonus to your AC. You use this spell as a reaction in battle, and it will last till the start of your next turn.
Other Bonuses to AC
Here are some extra ways to up your AC in the heat of combat!
You gain a bonus to AC by taking cover behind an object or structure. Half cover gives you a +2 bonus to AC. Three-quarters cover gives you a +5 to your AC. Finally, full cover makes it so you can’t be directly targeted by spells!
Player tip: If an enemy uses cover to defend from your attacks, try targeting them indirectly. If you have an area of effect spell, you can use it to hit them even if they have full cover.
The Dodge action doesn’t increase your AC, but it does cause disadvantage on attacks against you. If you need to survive, it’s a great action since AC can’t always save you. It’s good to try to have extra hit points.
To Sum It Up
Now you know that Armor Class (AC) determines a character’s ability to block or dodge attacks. Armor proficiency and armor type affect the AC calculation. You can also utilize class features and Magic to increase your AC. But remember, a high AC does not always guarantee protection from all attacks.
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