Armor Class

Your Armor Class (AC) represents how hard it is for opponents to land a solid, damaging blow on you. It’s the attack roll result that an opponent needs to achieve to hit you. Your AC is equal to the following:
10 + armor bonus + shield bonus + Dexterity modifier + size modifier + natural armor + deflection modifier + misc modifier

Armor Bonus

Your armor bonus is typically provided by actual armor. Magical armor may have an Enhancement Bonus bonus, but that bonus does not apply directly to the wearer. It instead increases the armor bonus provided to the wearer. Armor bonuses do not stack with each other. If a player is receiving an armor bonus from multiple sources, only the largest value is used.

Shield Bonus

Your shield bonus is typically provided by a shield. Magical shields may have an Enhancement Bonus bonus, but that bonus does not apply directly to the wearer. It instead increases the shield bonus provided to the wearer. Shield bonuses do not stack with each other. If a player is receiving a shield bonus from multiple sources, only the largest value is used.

Dexterity Modifier

Your Dexterity modifier is applied to your armor class, but only within the limits of your equipped armor and shield. The lowest Maximum Dex Bonus between your armor and shield is the maximum value that can be added by your dexterity to your armor class. Different qualities and materials may increase the maximum dexterity allowed by a given set of armor or shield.

Size Modifier

If your size is larger or smaller than medium, you apply a bonus or penalty to your armor class.

Natural Armor

Natural armor represents the bonus to armor class provided by a creature's tough hide. This bonus does not stack with itself; only the highest natural armor bonus is used.

Deflection Modifier

A deflection modifier is typically provided by magical items and effects. This bonus does not stack with itself; only the highest natural armor bonus is used.

Dodge Modifier

A dodge bonus improves Armor Class (and sometimes Reflex Saves) resulting from physical skill at avoiding blows and other ill effects. Dodge bonuses are never granted by spells or magic items. Any situation or effect (except wearing armor) that negates a character's Dexterity bonus also negates any dodge bonuses the character may have. Dodge bonuses stack with all other bonuses to AC, even other dodge bonuses. Dodge bonuses apply against touch attacks.

Misc Modifier

Any other modifiers go here. Modifiers without a type stack with all other modifiers, unless the source of the modifier explicitly states otherwise.

Touch Armor Class

Some attacks disregard armor, including shields and natural armor. In these cases, the attacker makes a touch attack roll (either ranged or melee). When you are the target of a touch attack, your AC doesn’t include any armor bonus, shield bonus, or natural armor bonus. All other modifiers, such as your size modifier, Dexterity modifier, and deflection bonus (if any) apply normally. Your Touch AC is calculated as follows:
10 + Dexterity modifier + size modifier + deflection modifier + dodge modifier + misc modifier

Flat-Footed Armor Class

Sometimes you can’t use your Dexterity bonus (if you have one). If you can’t react to a blow, you can’t use your Dexterity or Dodge bonus to AC, and are considered flat footed. Your Flat-Footed AC is calculated as follows:
10 + armor bonus + shield bonus + size modifier + natural armor + deflection modifier + misc modifier