🔱☂️ Defense: Armor Class - JulTob/DnD GitHub Wiki

Your Armor Class (AC)represents how well your character avoids being wounded in battle.

Armor Class (AC)

AC is the target number attackers must $\color{RED}meet$ or beat to hit you.

You set AC by choosing one base formula, then applying modifiers (like a shield, cover).

How you get your AC

♔1) Unarmored (default)

  • Without armour or a shield, your character's AC equals 10 + his or her Dexterity modifier.
  • $$Base AC = 10 + DEX mod$$
    Use this when you’re not wearing armor and no other feature sets your base AC.

♕2) Armor (Light / Medium / Heavy)

  • Each armor sets your base AC (some add DEX up to a cap).
  • Strength requirement: if you don’t meet it, your Speed –10 ft while wearing that armor.
  • Some armors impose Stealth (Disadvantage).

♖3) Features & Spells that set base AC

  • Examples: Mage Armor (base 13 + DEX), class features like Unarmored Defense, some natural armor traits.

  • Important: if multiple things set a base AC, you choose one at a time—they don’t stack.

⛨ Shield

  • +2 bonus to AC while you wield it. Requires shield training.

Wearing armor (or a shield) without training

If you use Light/Medium/Heavy armor (or a shield) without proficiency:

  • You have Disadvantage on any d20 Test involving STR or DEX.
  • If you can cast spells, you can’t cast them while wearing that armor/shield.

Cover (pairs with AC)

  • Half cover: +2 bonus to AC and DEX saves.
  • Three-quarters cover: +5 bonus to AC and DEX saves.
  • Total cover: you can’t be targeted directly. Use only the best degree if multiple apply.

Quick reference — common base AC formulas

Pick one base AC, then add shield if applicable.

  • Unarmored: 10 + DEX
  • Light armor: 11–12 + DEX (e.g., Leather 11+DEX, Studded 12+DEX)
  • Medium armor: 12–15 + DEX (max +2) (e.g., Chain Shirt 13+DEX(≤+2), Half Plate 15+DEX(≤+2))
  • Heavy armor: fixed 14–18 (e.g., Chain Mail 16, Plate 18), may have STR req and Stealth (Disadv.)
  • Mage Armor (spell): 13 + DEX (no armor worn)

Don/Doff: category determines how long it takes to put on or remove armor; check the Equipment table if timing matters in play.

Worked examples

  • Rogue in Studded Leather + Shield:
    Base 12 + DEX (+4) = 16, + 2 shield = 18.
    (If the rogue lacks shield training, they suffer the training penalties above.)

  • Cleric in Chain Mail on a road chase with STR 12:
    Base 16; STR req not met → Speed –10 ft until they remove it or rest in different armor.

  • Wizard with Mage Armor:
    Base 13 + DEX. If they later don armor, Mage Armor ends.

Common pitfalls (fix these fast)

  • Dodge doesn’t raise AC. It gives Disadvantage to attacks vs you and Advantage on your DEX saves until your next turn; it ends if you’re Incapacitated or your Speed = 0.
  • Only one base AC at a time. If a feature or spell sets base AC, choose it instead of armor’s base AC—don’t add them together.
  • Cover stacks with AC; shields add to AC. But two shields don’t stack, and you still need proficiency for shields/armor.