Armor Class (AC)
Also known as: AC, defense, armor rating
Definition
A defensive stat representing how hard a character is to hit in combat. Attack rolls must meet or exceed the target's AC to deal damage.
How it works in different systems
D&D 5e: AC = 10 + DEX mod (unarmored). Armor provides base AC. Shields add +2.
Call of Cthulhu 7e: No AC - attacks opposed by Dodge or Fighting. Armor reduces damage taken.
Vampire V5: No AC - attacks contested. Defense pools instead of static AC.
Savage Worlds: Parry (melee defense) and Toughness (damage resistance) instead of unified AC.
Example
“The knight has AC 18 (plate armor + shield). You roll 15 to hit - that's less than 18, so your attack bounces off their armor!”
Common Mistakes
- Forgetting that meeting AC is a hit (it's 'meet or beat')
- Not knowing what contributes to AC (armor, DEX, shields, magic, class features)
- Thinking higher AC makes you immune (nat 20 always hits)