Armor Class (AC) is one of the core defensive numbers in Dungeons & Dragons 5th Edition, representing how hard it is to hit a creature or character. Base AC refers to the starting defensive value a creature has before additional modifiers from Dexterity, class features, spells, or environmental effects are applied. In 5th Edition, base AC values are determined primarily by the type of creature and its natural armor, armor worn, or innate defensive traits. Understanding how base AC works, how it is calculated each round, and how bonuses and penalties affect it is essential for both players and Dungeon Masters during combat and character building.
How AC Is Calculated in 5e
In D&D 5e, AC is not a fixed static number for most characters; it is the result of several potential components added together. The basic formula is:
10 + Dexterity modifier + armor bonus (if any) + shield bonus (if active) + other modifiers
Unarmored characters such as wizards typically rely on 10 + Dexterity modifier for AC, while fighters in medium or heavy armor add their armor’s base AC value. Some creatures have a natural armor score listed in their stat block, replacing or supplementing manufactured armor. Other factors such as the Dodge action, the Shield spell, and certain class features can temporarily modify AC.
Base AC by Armor Type
Different types of armor provide distinct base AC values, and many of these values have remained consistent across editions, making them familiar to veteran players. Below is a concise breakdown of standard armor categories and their base AC in 5th Edition.
Light Armor
Light armor provides modest protection while allowing full mobility. It is commonly worn by rogues and some spellcasters.
- Padded: 11 + Dexterity modifier
- Leather: 11 + Dexterity modifier
- Studded leather: 12 + Dexterity modifier
Medium Armor
Medium armor offers better protection but may impose minor movement or ability restrictions.
- Hide: 12 + Dexterity modifier
- Chain shirt: 13 + Dexterity modifier
- Scale mail: 14 + Dexterity modifier
- Breastplate: 14 + Dexterity modifier
- Half plate: 15 + Dexterity modifier
Heavy Armor
Heavy armor delivers high protection at the cost of speed and agility.
- Ring mail: 14 + Dexterity modifier
- Chain mail: 16 + Dexterity modifier
- Splint: 17 + Dexterity modifier
- Plate: 18 + Dexterity modifier
Natural Armor and Unarmored Defense
Many monsters do not wear armor and instead have natural armor explicitly listed in their stat block. A creature with natural armor uses that value in place of the standard armor calculation unless a spell or effect states otherwise. Monks and certain other unarmored combatants often use an unarmored defense formula, typically calculated as 10 + Dexterity modifier + Wisdom (or other chosen ability) modifier while not wearing armor or using a shield.
Temporary and Situational Modifiers
AC can be raised or lowered by spells, class features, and special actions. The following table summarizes common temporary and conditional modifiers that affect AC in play.
| Modifier Type | Effect on AC | Typical Duration | Source |
|---|---|---|---|
| Dodge action | +5 until start of next turn | 1 round | Player class feature |
| Shield spell | +5 until start of next turn | 1 round | Wizard/sorcerer spell |
| Mage armor | 13 + Dexterity modifier | Concentration, 1 hour | 1st-level spell |
| Barkskin | 13 + Wisdom modifier (natural armor) | Concentration, 1 hour | 2nd-level spell |
| Shield (magic item) | +2 to AC | Continuous while attuned | Item property |
| Protection from spells/energy damage | +10 to AC vs. one damage type | Concentration, 1 minute | Higher-level spell |
Optional Rules and DM Variants
Tables and groups may use alternative AC rules depending on their playstyle. Common variants include:
- Heroic tier AC scaling, where base AC values are lowered and bonuses are increased to reduce lethality.
- Simplified AC, using a fixed list or flat values for monsters to streamline combat.
- No-calculation AC, where the DM simply states AC and players always roll to hit without modifiers, though this is rare in optimized play.
Common Misconceptions
Because AC is frequently discussed, several misunderstandings persist. AC does not represent only how much armor you wear; it reflects a combination of armor, agility, luck, and supernatural defenses. A high Dexterity modifier can dramatically improve AC even with light or no armor, so lightly armored characters can still be difficult to hit. Conversely, wearing heavy armor does not guarantee invulnerability, as penalties to Dexterity or effects that ignore armor can quickly make a heavily armored target fragile. Finally, many effects that grant resistance or immunity do not increase AC; they change damage calculations or attack rolls in different ways.
Strategic Considerations for Players
When building a character, players should consider how AC fits into their overall defensive plan. Armor choice affects not only AC but also speed, spellcasting components, and stealth checks. Wizards and other casters who rely on 10 + Dexterity for AC must weigh the benefits of shields or mage armor against the risks of opportunity attacks. Fighters and paladins using heavy plate gain substantial AC but may need to invest in Strength for effective weapon use and consider mobility options to avoid being kited. Monks and Dexterity-focused rogues usually avoid armor entirely, relying on unarmored defense and mobility to stay out of harm’s way.
Strategic Considerations for DMs
For DMs, understanding base AC values helps in designing balanced encounters. Using stat blocks as written ensures consistent defensive values, while homebrew adjustments should be tested at the table to avoid trivializing combat or making it overly punishing. When converting monsters between editions, AC values should be recalibrated carefully, as calculation methods differ significantly. DMs may also introduce environment-based modifiers, such as partial cover, darkness, or battlefield terrain, to adjust AC logically within the fiction.
Frequently Asked Questions
- Can AC ever be 0 or negative? No, AC cannot drop below 0 by normal means. Even with heavy penalties, a creature retains an AC of 0 rather than negative numbers in official rules.
- Does natural healing or resting change base AC? No, base AC is a creature’s static defensive value; temporary changes come from spells, conditions, or effects, not recovery.
- Can multiple sources of flat bonus armor stack? In most cases, only the best flat bonus applies. For example, a shield and mage armor do not stack; the higher value is typically used, and specific exceptions are rare and clearly stated.
- Do magic weapons affect AC? Generally, magic weapons affect attack rolls and damage, not AC, unless the weapon description or a specific feature states otherwise.
Bottom Line
Base AC in 5e is the foundation of a character or monster’s defense before Dexterity, class features, spells, and items are added. While light armor favors mobility, heavy armor emphasizes durability, and unarmored options reward ability scores and playstyle. When combined with temporary modifiers and tactical decisions, AC becomes a central element of defense and encounter design. Understanding how base AC works and how it interacts with the rest of the rules ensures smoother play, fairer adjudications, and more informed choices at the table.