Armor Class (AC) Calculator
Calculate and understand your character's defensive capabilities in tabletop RPGs.
AC Calculation Inputs
Your Armor Class Breakdown
Total AC = Base Armor + Dexterity Modifier + Shield Bonus + Other Bonuses. Some armor types may have limits on how much Dexterity bonus they allow.
What is Armor Class (AC)?
Armor Class (AC) is a fundamental statistic in many tabletop role-playing games (TTRPGs), most notably in Dungeons & Dragons (D&D). It represents a character's or creature's overall ability to avoid being hit by attacks. Think of it as a target number; when an attacker rolls an attack roll, they need to meet or exceed your AC to land a successful hit. A higher AC means a character is harder to hit.
Understanding AC is crucial for both players and Game Masters (GMs). Players want to maximize their AC to survive combat encounters, while GMs need to accurately calculate the AC of monsters and NPCs to run the game effectively. Misunderstandings about AC can lead to unbalanced encounters or characters that are either too vulnerable or unfairly difficult to damage.
The AC calculation is not always a simple sum. Different types of armor may impose restrictions on the Dexterity bonus that can be applied, and certain spells or abilities can temporarily alter AC. This armor class calculator aims to simplify the primary calculation, but always remember to consult your specific game's rules for nuances.
Armor Class (AC) Formula and Explanation
The core formula for calculating Armor Class is generally additive, combining various sources of defense.
Formula: Total AC = Base Armor Value + Dexterity Modifier + Shield Bonus + Other Bonuses
Let's break down the components:
| Variable | Meaning | Unit / Type | Typical Range |
|---|---|---|---|
| Base Armor Value | The inherent defensive rating provided by the armor worn (e.g., leather, chain mail, plate). | Unitless (Armor Rating) | 0 (unarmored) to 19+ (full plate with enchantments) |
| Dexterity Modifier | The bonus or penalty derived from a character's Dexterity score. Higher Dexterity generally improves dodging ability. | Unitless (Modifier Score) | -5 to +5+ (depending on system and score) |
| Shield Bonus | An additional AC bonus granted by actively using a shield. | Unitless (Bonus Points) | 0 to +5+ |
| Other Bonuses | Miscellaneous AC improvements from spells (like Shield of Faith), class features, magic items, or specific feats. | Unitless (Bonus Points) | Varies greatly, can be temporary or permanent |
Practical Examples
Example 1: The Nimble Rogue
A rogue wearing light armor and relying on their high Dexterity.
- Inputs:
- Base Armor Value (Studded Leather): 12
- Dexterity Modifier: +4
- Shield Bonus: 0 (dual-wielding daggers)
- Other Bonuses: 0
Calculation: 12 (Base Armor) + 4 (Dex Mod) + 0 (Shield) + 0 (Other) = 16
Result: The rogue's Total AC is 16.
Example 2: The Heavily Armored Knight
A heavily armored warrior with a shield.
- Inputs:
- Base Armor Value (Plate Mail): 18
- Dexterity Modifier: +1 (plate mail often restricts Dex bonus)
- Shield Bonus: +2 (wielding a tower shield)
- Other Bonuses: +1 (from a magical amulet)
Calculation: 18 (Base Armor) + 1 (Dex Mod) + 2 (Shield) + 1 (Other) = 22
Result: The knight's Total AC is 22.
How to Use This Armor Class Calculator
- Identify Your Base Armor: Determine the AC value provided by the armor your character is wearing. If unarmored, this is typically 10 (in D&D 5e) or based on Dexterity alone.
- Find Your Dexterity Modifier: Calculate or look up your character's Dexterity modifier based on their Dexterity score.
- Add Shield Bonus (If Applicable): If your character is wielding a shield, enter its AC bonus value.
- Include Other Bonuses: Add any AC bonuses from spells, abilities, magic items, or other sources.
- Calculate: Click the "Calculate AC" button.
- Interpret Results: The calculator will display your total AC and the breakdown of each contributing factor. A higher number indicates better defense.
Unit Selection: For AC calculations, all inputs are typically unitless modifiers or ratings. Therefore, a unit switcher is not necessary for this calculator. The values represent abstract defensive capabilities within the game's rules.
Key Factors That Affect Armor Class
- Armor Type: Light, medium, and heavy armor provide different base AC values and may have varying impacts on speed, stealth, and Dexterity application.
- Dexterity Score: Characters with higher Dexterity benefit more from Dexterity-based AC bonuses, especially when wearing lighter armors.
- Shield Use: Actively wielding a shield significantly increases AC but may prevent the use of two-handed weapons or certain class features.
- Magic Items & Enchantments: Magical armor, shields, rings of protection, and cloaks of displacement can all provide substantial AC bonuses.
- Spells & Abilities: Spells like Shield or Mage Armor, and class features like a Monk's Unarmored Defense or a Barbarian's Rage, can significantly alter AC.
- Cover: In many systems, standing behind objects or in difficult terrain can grant an AC bonus (cover) by making the character harder to target.
- Size: While less common as a direct AC modifier, creature size can sometimes influence game mechanics related to hitting them.
- Targeting Rules: Some special attacks or abilities might ignore AC or target different defenses (like saving throws).
FAQ
A: Not necessarily. Heavy armor (like plate mail) often has an 'Armor Check Penalty' or explicitly states that it doesn't add any Dexterity bonus. Medium armor might cap the Dexterity bonus you can add (e.g., max +2). Light armor typically adds the full modifier. Always check the specific armor's description.
A: If you're unarmored, your Base Armor Value is often 10 in systems like D&D 5e. Your AC would then be calculated based on your Dexterity modifier, shield, and any other bonuses (like from a Monk's or Barbarian's class features).
A: It's highly unlikely in most common TTRPGs. Even unarmored characters usually start with a base AC of 10, and negative Dexterity modifiers are typically small. AC represents a target number to hit, so a very low score just means the character is easy to hit.
A: AC is used to determine if an attack hits. Saving Throws are used to resist the effects of spells, traps, and other hazards that often require a roll against a target number (DC – Difficulty Class) to avoid or mitigate harm.
A: AC typically applies only to attack rolls made with weapons or other physical means. Spells and other magical effects usually require a "Saving Throw" instead of an attack roll, bypassing AC. Some specific spells might be exceptions.
A: You generally only benefit from the heaviest armor you are wearing that you are proficient with. Wearing multiple sets of armor is usually cumbersome and doesn't stack benefits; it might even impose penalties.
A: Cover provides a bonus to AC and Dexterity saving throws. For example, partial cover might grant +2 AC, three-quarters cover +5 AC, and total cover makes you unable to be targeted directly. This is separate from your calculated AC but affects whether attacks hit you.
A: While theoretically possible with stacking numerous magical effects, most game systems have implicit or explicit caps, or the items/spells required become extremely rare and powerful, balancing the game. Focus on reaching a reasonable AC for your level.