Armor class (AC) is a number representing a creature's ability to avoid being hit in combat. An opponent's attack roll must equal or exceed the target creature's AC to hit it. AC = 10 + armor bonus + shield bonus + dodge bonus + natural armor bonus + deflection bonus + other bonuses Effective AC = 10 + armor bonus + shield bonus + dodge bonus + natural armor bonus + deflection bonus + other bonuses + active armour (any reductions in the opponents AB (usually as a result of an offensive action)) The average, unarmored peasant has an AC of 10.