5E Ac Calculator

Calculate Armor Class in Dungeons and Dragons 5e with armor, Dexterity, shield, fighting style, cover, magic, and custom bonuses.

Results and hit chance

See your total AC, rules breakdown, and the exact chance to be hit by common attack bonuses.

Hit chance is calculated using standard d20 logic with a natural 1 always missing and a natural 20 always hitting.

Expert Guide to the 5e AC Calculator

Armor Class, usually shortened to AC, is one of the most important defensive numbers in Dungeons and Dragons 5e. It determines how hard your character is to hit when an enemy makes an attack roll. A reliable 5e AC calculator helps players, dungeon masters, and theorycrafters make faster and more accurate decisions when choosing armor, assigning ability scores, comparing subclasses, or planning equipment upgrades. If you have ever asked whether a shield is worth it, whether half plate beats studded leather for your build, or how much a point of AC really matters, this guide will help you understand both the rules and the math.

In simple terms, AC is the target number an attacker must meet or exceed with an attack roll to land a hit. Most attack rolls in 5e use a twenty-sided die plus an attack bonus. If the total equals or beats your AC, the attack hits. Because every point of AC raises that target, even a small increase can noticeably reduce incoming damage over time. That is why AC is one of the most efficient defensive levers in the game, especially for front-line characters who expect to be attacked repeatedly across multiple encounters.

How a 5e AC calculator works

A good calculator starts with the armor formula that applies to your character. In 5e, not every build calculates AC the same way. Some characters wear light, medium, or heavy armor. Others rely on special formulas such as Mage Armor, Barbarian Unarmored Defense, Monk Unarmored Defense, Draconic Resilience, or racial natural armor. The calculator above lets you choose the most common official formulas and then layers in the most frequent situational modifiers:

• Base armor value from worn armor or a special defensive feature.
• Dexterity modifier, which may be fully applied, capped, or ignored depending on the armor.
• Secondary modifier for classes like Barbarian and Monk.
• Shield bonus, usually +2 AC.
• Magic bonus from enhanced armor or protective items.
• Defense fighting style, typically +1 AC while wearing armor.
• Cover, which can add +2 or +5 to AC against many attacks.
• Miscellaneous bonuses from spells, features, or campaign-specific effects.

When all of those factors are added correctly, you get a total AC that reflects your actual defensive setup at the table. The chart then goes a step further and shows how often enemies with certain attack bonuses will hit you. That is what turns a raw AC number into meaningful tactical information.

The most useful way to evaluate AC is not to ask “What number do I have?” but “How much does this number reduce enemy hit probability over the course of a fight?”

Core AC formulas every player should know

The default AC formula for an unarmored creature is 10 + Dexterity modifier. From there, specific armors and features replace or modify that baseline. Light armor adds your full Dexterity modifier. Medium armor adds Dexterity up to a maximum of +2. Heavy armor ignores Dexterity altogether. Special class features can replace the standard formula entirely.

Defense option	Base rule	Dexterity rule	Typical user
Unarmored	10	Full Dex	Common baseline for any creature not using armor
Mage Armor	13	Full Dex	Wizards, Sorcerers, Warlocks
Leather	11	Full Dex	Stealth-oriented light armor builds
Studded Leather	12	Full Dex	Rogues, Rangers, Dex Fighters
Chain Shirt	13	Dex max +2	Medium armor users
Breastplate	14	Dex max +2	Medium armor users seeking solid AC
Half Plate	15	Dex max +2	High AC medium armor builds
Chain Mail	16	No Dex	Strength-based heavy armor users
Plate	18	No Dex	Top-end heavy armor baseline
Barbarian Unarmored Defense	10	Dex + Con	Barbarian
Monk Unarmored Defense	10	Dex + Wis	Monk

This comparison shows why the right formula matters so much. A Barbarian with Dexterity +2 and Constitution +3 has an AC of 15 while unarmored before shields or magic. A Monk with Dexterity +4 and Wisdom +3 reaches 17 before magical support. By contrast, a Dexterity-based Rogue in studded leather with Dexterity +4 has AC 16 before any magical improvement.

What one point of AC is really worth

Many players underestimate the power of a single AC increase because it looks small on paper. In reality, one point of AC usually shifts enemy hit probability by 5 percentage points on a d20 roll, subject to the natural 1 and natural 20 rules. Over many attacks, that can be a large reduction in incoming damage. If an enemy attacks you ten times in a combat arc and your AC causes one of those attacks to miss instead of hit, the benefit can easily exceed the value of a small damage boost or situational offensive rider.

To make that idea concrete, here is a probability table based on standard 5e attack rules. These are exact hit chances, not estimates.

Enemy attack bonus	Vs AC 12	Vs AC 15	Vs AC 18	Vs AC 21
+3	60%	45%	30%	15%
+5	70%	55%	40%	25%
+8	85%	70%	55%	40%
+11	95%	85%	70%	55%

The table makes two strategic truths obvious. First, AC is extremely valuable in the middle ranges where many monsters live. Raising AC from 15 to 18 against a +5 attacker cuts hit probability from 55% to 40%, which is a relative reduction of more than one-quarter. Second, AC does not become useless at high levels, but it does become less absolute because monster attack bonuses increase. Your goal is not invulnerability. Your goal is to force more misses than your party would otherwise suffer.

Choosing the best armor for your build

The best armor choice depends on your ability scores, class features, budget, and play style. A 5e AC calculator is most valuable when comparing these tradeoffs quickly. Here are some common examples:

1. Dexterity builds: If your Dexterity modifier is high, light armor often scales well. Studded leather with Dex +4 gives AC 16, and with a shield on an eligible build that can jump to 18.
2. Balanced martial builds: Medium armor is ideal when your Dexterity is decent but not exceptional. Half plate with Dex +2 gives 17 AC before shield or magic, a very efficient benchmark.
3. Strength front liners: Heavy armor is excellent when Dexterity is low. Plate starts at 18 AC and does not care whether your Dex modifier is +0 or negative.
4. Unarmored specialists: Monk and Barbarian can become surprisingly durable if their core secondary stats are developed properly.
5. Arcane casters: Mage Armor can be a major boost for characters who expect to be targeted and do not wear armor normally.

When deciding between options, always compare your likely real combat setup rather than the armor line by itself. For example, breastplate plus shield may be better for one build than half plate without a shield. Likewise, a character who can reliably maintain Mage Armor may outperform low-tier mundane armor options despite not wearing any physical armor at all.

Why shields, cover, and magic matter so much

Some of the strongest AC gains in 5e come from simple additions rather than changing armor categories. A shield adds +2 AC, which is equivalent to a 10 percentage point reduction in hit chance against many attacks. Half cover gives another +2. Three-quarters cover gives +5, which can be dramatic in ranged fights. Magical armor bonuses and protective items further compound the effect.

This is also why AC calculators should support layered bonuses. A character in plate armor with a shield, a +1 magic bonus, and half cover can move from a normal AC of 18 to a situational AC of 23. Against some attack bonuses, that can cut expected hits nearly in half. Even if the situation is temporary, understanding the exact defensive swing helps both players and dungeon masters make better tactical choices.

Common mistakes players make when calculating AC

• Adding full Dexterity to medium armor when the armor caps Dexterity at +2.
• Adding Dexterity to heavy armor, which heavy armor does not allow.
• Stacking incompatible AC formulas such as combining Mage Armor with normal armor or trying to add multiple base calculations at once.
• Forgetting shield restrictions on certain concepts, roleplay choices, or hand-usage plans.
• Ignoring situational bonuses like cover, fighting style, or temporary effects.
• Misreading class features such as Barbarian and Monk unarmored formulas, which depend on different secondary abilities.

A dedicated calculator helps eliminate these errors by making the formula visible and by showing a line-by-line breakdown of the final result.

How to interpret hit chance charts

The chart generated above translates your AC into a more intuitive metric: the chance that a creature with a given attack bonus will hit you. This matters because players often evaluate survivability in terms of “How likely am I to be hit each round?” rather than “What is my AC total?” By comparing multiple enemy bonuses at once, the chart helps you answer practical questions such as:

• Is my current AC high enough for the tier of play?
• How much does a shield improve my durability against common threats?
• Does upgrading from breastplate to half plate justify the cost or stealth tradeoff?
• How much does cover matter during ranged combat?
• Will a magical +1 bonus noticeably change encounter outcomes?

Because the d20 system is linear, each AC point usually shifts hit probability by 5 percentage points until the natural 1 and natural 20 boundaries start to matter. That makes AC one of the easiest defensive stats to model accurately.

Strategic benchmarks for practical play

While there is no single perfect AC number for all campaigns, practical benchmarks help. Early-game back-line casters often feel comfortable around AC 13 to 15 if they stay protected by positioning. Mid-line characters often aim for AC 15 to 17. Front-line defenders are commonly strongest at AC 18 and above, especially if they expect multiple melee attacks each round. Reaching AC 20 or higher through shields, magic, and class features is a major milestone because it pushes many average enemies into uncomfortable hit rates.

That said, AC is only one layer of defense. Hit points, resistances, mobility, saving throws, temporary hit points, concealment, battlefield control, and healing all matter. A smart optimizer treats AC as part of a complete defensive profile, not as the only answer.

Probability resources for deeper study

If you want to understand the math behind hit chance, expected outcomes, and probability distributions more deeply, these academic and government resources are useful starting points:

• NIST Engineering Statistics Handbook for foundational probability and statistical reasoning.
• Penn State STAT 414 Probability Theory for a structured university-level overview of probability.
• UC Berkeley probability notes on chance for intuitive explanations of probability concepts.

Final thoughts on using a 5e AC calculator

A 5e AC calculator is more than a convenience tool. It is a decision aid that turns rules text into clear tactical information. By calculating the correct armor formula, applying real modifiers, and translating the result into exact hit percentages, it shows the true value of armor, shields, class features, and cover. Whether you are building a durable paladin, optimizing a stealth ranger, planning a monk, or simply trying to understand whether Mage Armor is worth the spell slot, the key is to compare actual outcomes rather than guessing.

Use the calculator whenever your equipment changes, your ability scores improve, or your party expects different types of threats. The best AC is not always the highest theoretical value. It is the one that fits your character, your role in the party, and the practical realities of your campaign. When you combine good rules knowledge with accurate probability, you make stronger characters and smarter tactical choices.