Armor Rules and Types in D&D
Armor is one of the most consequential decisions a D&D character makes at level 1, and it quietly shapes every combat encounter that follows. The system governs how difficult a character is to hit, which ability scores matter for defense, and whether a particular build even functions as intended. This page covers how armor is defined in the rules, how Armor Class is calculated, the three main armor categories, and the practical moments where armor choices become genuinely complicated.
Definition and scope
In Dungeons & Dragons 5th Edition, armor is a category of equipment that establishes a character's Armor Class (AC) — the number an attacker must meet or exceed on a d20 attack roll to deal damage. The Player's Handbook (published by Wizards of the Coast) defines armor across three broad categories: light, medium, and heavy. A fourth option, shields, adds a flat +2 to AC regardless of which armor type is worn.
The system also enforces proficiency requirements. A character who wears armor without proficiency — say, a Wizard who somehow acquires a suit of plate — suffers meaningful penalties: disadvantage on Strength checks, Strength saving throws, and Dexterity saving throws, and the inability to cast spells. Proficiency access is class-dependent, with Fighters and Paladins receiving all armor types, while Rogues and Rangers stop at medium.
How it works
AC is not a single static number — it's a calculation, and the formula depends entirely on which armor is worn.
- Light armor (Leather, Studded Leather): Base AC value plus the character's full Dexterity modifier. Studded Leather sets the base at 12, so a character with a +3 Dexterity modifier reaches AC 15.
- Medium armor (Chain Shirt, Scale Mail, Breastplate, Half Plate): Base AC value plus the Dexterity modifier, capped at +2. A Breastplate (base 14) with a +5 Dexterity modifier still yields only AC 16, not 19.
- Heavy armor (Ring Mail, Chain Mail, Splint, Plate): A fixed AC value — no Dexterity modifier applied at all. Plate armor sets AC at 18, period.
Shields stack additively with any armor type, making a Fighter in Plate plus Shield a baseline AC 20 — before any magical enhancements.
There's also the Unarmored Defense feature, carried by Barbarians and Monks as a class ability. A Barbarian calculates AC as 10 + Dexterity modifier + Constitution modifier. A Monk uses 10 + Dexterity modifier + Wisdom modifier. Neither wears armor to activate this; equipping any armor immediately switches the calculation back to the armor's formula.
The full breakdown of how these mechanics interact rewards careful reading — especially for multiclassing scenarios, where a Monk-Barbarian combination raises questions about which Unarmored Defense formula applies. (Only one can; the Player's Handbook is explicit that a character can't benefit from both simultaneously.)
Common scenarios
The Dexterity-based character: A Rogue or Ranger with a +4 or +5 Dexterity modifier often finds that Studded Leather (base 12 + full Dex) outperforms or matches medium armor's capped calculation. Studded Leather with +5 Dex equals AC 17. The best non-magical medium armor available at most tier-1 play is a Breastplate, which caps at AC 16. Studded Leather wins — and costs significantly less gold.
The Strength-dumped Cleric: Clerics with heavy armor proficiency still need a Strength score of 15 to wear Plate without a movement speed penalty (reduced by 10 feet per the Player's Handbook). A character built around Wisdom and Constitution who ignores Strength can end up stuck at Chain Mail (AC 16) or paying the speed tax.
The caster who wants survivability: A Bladesinger Wizard can use their Bladesong feature to add their Intelligence modifier to AC while it's active, stacking on top of the light armor they can wear — an unusual route to competitive AC for a primary spellcaster. This appears in the Sword Coast Adventurer's Guide (also Wizards of the Coast).
More common questions about how armor interacts with specific spells and features come up around the Mage Armor spell, which sets AC at 13 + Dexterity modifier and explicitly doesn't work if the target is wearing armor.
Decision boundaries
The choice between armor types isn't purely mechanical — it's also a resource question and a campaign question.
Light vs. Medium: A character with Dexterity below +2 gains nothing from light armor over medium. A character with Dexterity of +3 or higher starts to see light armor become competitive, and at +4 or +5, light armor frequently wins on raw AC unless magical medium armor is available.
Medium vs. Heavy: The Medium Armor Master feat (Player's Handbook) raises the Dexterity cap on medium armor from +2 to +3, and removes the disadvantage on Stealth checks that several medium armors impose. For a character with a +3 Dexterity modifier, this feat can push medium armor to AC 17 — matching non-magical Splint and nearly matching Plate. Heavy armor requires no feat to reach 18 AC, but it demands a 15 Strength score and costs 1,500 gold pieces for Plate. Both are significant constraints at early levels.
Magical armor: A +1 Chain Mail is AC 17. A +1 Breastplate with the Medium Armor Master feat is also AC 18 (14 base + 3 Dex cap + 1 enhancement). At that point, the gap between armor categories narrows considerably, and the choice shifts toward what a character can actually wear without penalties.
The scope of these rules within D&D's broader system extends to how armor interacts with conditions, cover mechanics, and specific monster abilities — making it one of the rules subsystems that rewards knowing the edges, not just the center.