Unlocking Armor Class: A Comprehensive Guide to AC in D&D 5e
Armor Class (AC) is a fundamental concept in Dungeons & Dragons 5th Edition (D&D 5e). It represents how difficult it is for an enemy to successfully hit a character in combat. Understanding how AC is calculated and modified is crucial for both players and Dungeon Masters (DMs) to effectively navigate the game’s combat system. This comprehensive guide will walk you through the intricacies of AC calculation, providing step-by-step instructions and examples to ensure you grasp this essential mechanic.
## What is Armor Class?
In essence, Armor Class is a target number. When an attacker attempts to hit a creature, they roll a d20 (a 20-sided die) and add any relevant modifiers, such as their Strength modifier for melee attacks or Dexterity modifier for ranged attacks, and proficiency bonus if they are proficient with the weapon they are using. If the total result equals or exceeds the target creature’s AC, the attack hits. If the result is lower than the AC, the attack misses.
Therefore, a higher AC means a creature is harder to hit, representing better armor, natural defenses, or agility. Conversely, a lower AC means a creature is easier to hit, indicating a lack of protection.
## The Basic AC Calculation
The most basic way to determine a creature’s AC is through armor. However, other factors can significantly influence the final number. The core formula is:
**Base AC + Armor Bonus (if applicable) + Shield Bonus (if applicable) + Dexterity Modifier (if applicable) + Other Modifiers (if applicable)**
Let’s break down each component:
* **Base AC:** This is the starting AC value, often determined by whether a character is wearing armor or not. If not wearing armor, the base AC is often calculated using Dexterity, Constitution, or Wisdom. Some races and classes offer unique base AC calculations.
* **Armor Bonus:** This is the bonus to AC provided by the type of armor worn. Different armors offer different bonuses. For example, leather armor provides a lower bonus than plate armor.
* **Shield Bonus:** If a character is wielding a shield, they gain a +2 bonus to their AC.
* **Dexterity Modifier:** Some armors allow characters to add their Dexterity modifier to their AC. However, certain armors impose a limit on the maximum Dexterity bonus that can be applied. Medium armor, for instance, typically limits the Dexterity bonus to +2.
* **Other Modifiers:** This category encompasses a variety of bonuses and penalties from spells, class features, feats, and magical items that can affect AC. These modifiers are usually clearly defined in the relevant source.
## Step-by-Step AC Calculation Guide
Let’s go through a detailed, step-by-step guide to calculating AC, complete with examples:
**Step 1: Determine the Base AC**
The first step is to determine the base AC. This depends on whether the character is wearing armor and, if not, on their class and race features. Here are some common scenarios:
* **No Armor:** If a character is not wearing armor, their base AC is typically 10 + their Dexterity modifier. This is the most common starting point.
* **Barbarian:** Barbarians have a class feature called *Unarmored Defense* that allows them to calculate their AC as 10 + their Dexterity modifier + their Constitution modifier when they are not wearing armor. This makes them surprisingly durable even without conventional armor.
* **Monk:** Monks also have an *Unarmored Defense* feature. Their AC is calculated as 10 + their Dexterity modifier + their Wisdom modifier when they are not wearing armor.
* **Draconic Sorcerer:** Some Draconic Bloodline Sorcerers gain a base AC of 13 + their Dexterity modifier due to their draconic resilience, even when unarmored.
**Example 1: Rogue with no armor**
* A Rogue has a Dexterity score of 16, which grants a +3 Dexterity modifier.
* Since they are not wearing armor, their base AC is 10 + 3 = 13.
**Example 2: Barbarian with no armor**
* A Barbarian has a Dexterity score of 14 (+2 modifier) and a Constitution score of 16 (+3 modifier).
* Due to their *Unarmored Defense*, their base AC is 10 + 2 + 3 = 15.
**Step 2: Choose Armor (if applicable)**
If a character chooses to wear armor, the type of armor they select will affect their AC. Each type of armor provides a different base AC and may impose restrictions on the Dexterity bonus that can be added. Here’s a summary of common armor types:
* **Light Armor:**
* *Padded*: AC 11 + Dexterity modifier
* *Leather*: AC 11 + Dexterity modifier
* *Studded Leather*: AC 12 + Dexterity modifier
* **Medium Armor:**
* *Hide*: AC 12 + Dexterity modifier (maximum +2)
* *Chain Shirt*: AC 13 + Dexterity modifier (maximum +2)
* *Scale Mail*: AC 14 + Dexterity modifier (maximum +2)
* *Breastplate*: AC 14 + Dexterity modifier (maximum +2)
* *Half Plate*: AC 15 + Dexterity modifier (maximum +2)
* **Heavy Armor:**
* *Ring Mail*: AC 14
* *Chain Mail*: AC 16
* *Splint Mail*: AC 17
* *Plate Armor*: AC 18
Heavy armor does not allow the wearer to add their Dexterity modifier to their AC. Additionally, some armors impose a Strength requirement. If a character’s Strength score is lower than the required score, they have disadvantage on Strength checks, Strength saving throws, and their speed is reduced by 10 feet.
**Example 3: Fighter with Leather Armor**
* A Fighter has a Dexterity score of 14 (+2 modifier) and is wearing Leather Armor (AC 11 + Dexterity modifier).
* Their AC is 11 + 2 = 13.
**Example 4: Paladin with Half Plate**
* A Paladin has a Dexterity score of 16 (+3 modifier) and is wearing Half Plate (AC 15 + Dexterity modifier, maximum +2).
* Due to the limitation on Dexterity bonus, their AC is 15 + 2 = 17.
**Example 5: Fighter with Plate Armor**
* A Fighter has a Dexterity score of 12 (+1 modifier) and is wearing Plate Armor (AC 18).
* Since Plate Armor does not use dexterity, the final AC is 18.
**Step 3: Add Shield Bonus (if applicable)**
A shield provides a +2 bonus to AC. This bonus stacks with armor and other modifiers. A character must be proficient with shields to gain the bonus. Wielding a shield without proficiency imposes disadvantage on attack rolls, saving throws, and ability checks until proficiency is gained.
**Example 6: Fighter with Leather Armor and Shield**
* A Fighter has a Dexterity score of 14 (+2 modifier), is wearing Leather Armor (AC 11 + Dexterity modifier), and is wielding a shield (+2 bonus).
* Their AC is 11 + 2 + 2 = 15.
**Example 7: Paladin with Half Plate and Shield**
* A Paladin has a Dexterity score of 16 (+3 modifier), is wearing Half Plate (AC 15 + Dexterity modifier, maximum +2), and is wielding a shield (+2 bonus).
* Due to the limitation on Dexterity bonus, their AC is 15 + 2 + 2 = 19.
**Step 4: Apply Other Modifiers**
Numerous other factors can modify a character’s AC. These can come from spells, class features, feats, and magic items. It’s crucial to carefully read the descriptions of these features to understand how they affect AC.
Some common sources of AC modifiers include:
* **Spells:**
* *Shield* : As a reaction, you can use *Shield* to create a barrier of magical force that grants you +5 to AC until the start of your next turn, including against the triggering attack.
* *Mage Armor*: This spell provides a base AC of 13 + Dexterity modifier for creatures not wearing armor.
* *Barkskin*: The target’s skin becomes as tough as bark. Until the spell ends, the target’s AC can’t be less than 16, regardless of what kind of armor it is wearing.
* **Class Features:**
* *Defensive Fighting Style (Fighter, Paladin, Ranger)*: While you are wearing armor, you gain a +1 bonus to AC.
* **Feats:**
* *Fighting Initiate: Defense*. Same as Defensive Fighting Style. Grants +1 to AC while wearing armor.
* **Magic Items:**
* *Ring of Protection*: Provides a +1 bonus to AC and saving throws.
* *Armor of Magic*: Some magic armor provides a higher AC than standard armor of its type, or grants a bonus to AC. For example, +1 Plate Armor provides AC 19. These bonuses usually stack with a shield.
**Important Note:** Most bonuses to AC stack. However, bonuses from spells with the same name do NOT stack. You can’t cast *Shield* twice in the same turn to gain a +10 to AC.
**Example 8: Fighter with Plate Armor, Shield, and Ring of Protection**
* A Fighter is wearing Plate Armor (AC 18), wielding a shield (+2 bonus), and wearing a Ring of Protection (+1 bonus).
* Their AC is 18 + 2 + 1 = 21.
**Example 9: Monk with Mage Armor**
* A Monk has a Dexterity score of 16 (+3 modifier) and a Wisdom score of 14 (+2 modifier).
* Normally, their Unarmored Defense would provide an AC of 10 + 3 + 2 = 15.
* However, they cast *Mage Armor*, which provides a base AC of 13 + Dexterity modifier. This would be 13 + 3 = 16.
* The *Mage Armor* overrides the Unarmored Defense because it provides an explicit AC calculation. They can use the higher of the two.
**Example 10: Fighter with Plate Armor and Defensive Fighting Style**
* A Fighter is wearing Plate Armor (AC 18) and has the Defensive Fighting Style (+1 to AC).
* Their AC is 18 + 1 = 19.
## Unarmored Defense: Barbarians and Monks
As mentioned earlier, Barbarians and Monks have the *Unarmored Defense* feature, which allows them to calculate their AC without wearing armor. This feature is unique to these classes and provides an alternative way to achieve high AC.
* **Barbarian:** AC = 10 + Dexterity modifier + Constitution modifier
* **Monk:** AC = 10 + Dexterity modifier + Wisdom modifier
It’s important to note that these features only apply when the character is not wearing armor or using a shield. If a Barbarian or Monk chooses to wear armor, they cannot use their *Unarmored Defense* feature.
**Example 11: Barbarian with Unarmored Defense**
* A Barbarian has a Dexterity score of 14 (+2 modifier) and a Constitution score of 16 (+3 modifier).
* Their AC is 10 + 2 + 3 = 15.
**Example 12: Monk with Unarmored Defense**
* A Monk has a Dexterity score of 16 (+3 modifier) and a Wisdom score of 14 (+2 modifier).
* Their AC is 10 + 3 + 2 = 15.
## Natural Armor
Some creatures possess natural armor, which is a base AC value that is used in place of the standard 10 + Dexterity modifier. This is common among monsters and certain races. Natural armor is typically represented as a number, such as AC 14 (natural armor).
When calculating AC with natural armor, you simply use the given AC value. You do *not* add the Dexterity modifier to this value unless the creature’s description explicitly states that it does.
**Example 13: Lizardfolk**
* Lizardfolk have a natural armor of 13 + Dexterity modifier.
* A Lizardfolk has a Dexterity score of 12 (+1 modifier).
* Their AC is 13 + 1 = 14.
**Example 14: Monster with Natural Armor**
* A monster has an AC of 15 (natural armor).
* Its AC is simply 15, regardless of its Dexterity score.
## Situational Modifiers to AC
AC can also be affected by situational factors. These modifiers are typically temporary and depend on the specific circumstances of combat.
Some common situational modifiers include:
* **Cover:** Being behind cover grants a bonus to AC. Half cover provides a +2 bonus, three-quarters cover provides a +5 bonus, and total cover makes a creature impossible to target directly.
* **Prone:** A prone creature is easier to hit with ranged attacks, but harder to hit with melee attacks. Ranged attacks against a prone creature have disadvantage if the attacker is within 5 feet of the creature. Melee attacks against a prone creature have advantage.
* **Restrained:** A restrained creature has disadvantage on Dexterity saving throws, and attack rolls against it have advantage.
* **Incapacitated:** An incapacitated creature can’t take actions or reactions.
* **Unconscious:** An unconscious creature is incapacitated, prone, and unaware. Attack rolls against the creature have advantage, and any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.
* **Invisible:** Attack rolls against an invisible creature have disadvantage, and the invisible creature has advantage on attack rolls.
These situational modifiers can significantly affect the outcome of combat. It’s important to consider these factors when determining whether an attack will hit or miss.
**Example 15: Attacking a Creature Behind Half Cover**
* A creature has an AC of 16.
* The creature is behind half cover, granting a +2 bonus to AC.
* The effective AC becomes 16 + 2 = 18.
* An attacker needs to roll 18 or higher to hit the creature.
## Common Mistakes in AC Calculation
Several common mistakes can occur when calculating AC. Being aware of these mistakes can help you avoid errors and ensure accuracy.
* **Stacking Bonuses Incorrectly:** Be careful about stacking bonuses from the same source. As a general rule, bonuses from the same spell or ability do not stack. For example, you can’t benefit from *Shield* spell multiple times in the same round to gain a larger AC bonus.
* **Ignoring Armor Restrictions:** Some armors impose restrictions on the Dexterity bonus that can be applied. Make sure to adhere to these limitations when calculating AC.
* **Forgetting Shield Bonus:** It’s easy to forget the +2 bonus from wielding a shield. Always remember to add this bonus if the character is using a shield and is proficient with it.
* **Misunderstanding Natural Armor:** Natural armor is a base AC value and generally does not include a Dexterity bonus unless explicitly stated.
* **Confusing Base AC with Total AC:** Remember that base AC is just the starting point. The total AC is the base AC plus armor bonus, shield bonus, Dexterity modifier (if applicable), and other modifiers.
* **Not Factoring in Situational Modifiers:** Don’t forget to consider situational modifiers such as cover, prone, and other conditions that can affect AC.
## Tips for DMs
As a Dungeon Master, it’s your responsibility to accurately calculate the AC of creatures and NPCs. Here are some tips to help you manage AC effectively:
* **Keep a Record:** Maintain a record of each creature’s AC, including all relevant modifiers. This will save you time during combat.
* **Double-Check Calculations:** Always double-check your AC calculations to ensure accuracy. Mistakes can lead to unbalanced encounters and frustrated players.
* **Be Consistent:** Apply the same rules and calculations consistently across all creatures and NPCs.
* **Communicate Clearly:** Clearly communicate the AC of creatures to your players. This will help them make informed decisions during combat.
* **Use Tools:** Consider using online tools or character sheets to automate AC calculations.
## Conclusion
Understanding Armor Class is essential for playing and running D&D 5e effectively. By following this comprehensive guide, you can accurately calculate AC, account for modifiers, and avoid common mistakes. Whether you’re a player or a Dungeon Master, mastering AC will enhance your understanding of combat and improve your overall gaming experience. Practice these steps, and you’ll be well on your way to becoming an AC expert!