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Armor Class

Armor Class (AC) is the protective rating of a type of armor. Armor doesn't absorb damage — it prevents it by reducing the chance an attack lands in the first place. A fighter in full plate may be a slow-moving target, but penetrating the armor to cause any damage is no small task.

The scale

AC is measured on an inverted scale: lower numbers are better.

  • 10 = no armor (worst).
  • 0 = the reference value used by THAC0 (the "To Hit Armor Class 0" number).
  • Negative numbers = better armor; the most powerful magical armors can take a character below –10.

What modifies AC

  • Armor and shields are the base contributors.
  • High Dexterity grants a bonus to AC (see Combat Modifiers).
  • Magical items — a +1 shield improves AC by one beyond a normal shield (so AC 5 becomes AC 4, etc.).
  • Spells and abilities — many spells temporarily improve AC.

Stacking limits

You may not equip multiple magic items that provide the same kind of bonus — for example, two Rings of Protection, or a Ring of Protection alongside +1 Leather Armor. Only one applies.

Source: bgee/original_manuals/baldurs_gate_1_ee_mastering_melee_and_magic.pdf — "Armor Class", "Magical Items".