See also: Character Combat
Your Defenses represent your ability to avoid taking Damage and overcome attacks to the body and mind. You have three Defense Scores:
Reflex Defense: 10 + Heroic Level or Armor Bonus + Dexterity Modifier + Class Bonus + Size Modifier
Fortitude Defense: 10 + Heroic Level + Constitution Modifier + Class Bonus + Equipment Bonus
Will Defense: 10 + Heroic Level + Wisdom Modifier + Class Bonus
Your Species, Talents, Feats, and Actions may grant additional bonuses to one or more of these Defenses. For example, Gamorreans gain a +2 Species bonus to their Fortitude Defense, while a character with the Improved Defenses feat gains a +1 bonus to all three Defenses.
Reflex Defense
Your Reflex Defense (Abbreviated Reflex) represents how hard you are to hit in combat, and most attacks target a creature's Reflex Defense. If an opponent's Attack Roll equals or exceeds your Reflex Defense, the attack hits.
Heroic Level: Your Heroic Level is the sum of all levels you have in Heroic Classes (Jedi, Noble, Scoundrel, Scout, Soldier, Technician, and Force Prodigy) and Prestige Classes (Such as Ace Pilot or Sith Lord). It does not include levels in the Nonheroic class or Beast class.
Armor Bonus: Your Armor Bonus is determined by the Armor you wear. If you are wearing Armor, add your Armor Bonus to your Reflex Defense instead of your Heroic Level. This represents the difference between using your innate skill to avoid injury and counting on your Armor to absorb the damage from incoming attacks.
Dexterity Modifier: Nimble targets are more difficult to hit than slow ones. Add your Dexterity Modifier to your Reflex Defense. If you are Flat-Footed or unaware of an attack, you lose your Dexterity bonus (But not a penalty) to your Reflex Defense. If you are helpless (For example, knocked unconscious), calculate your Reflex Defense as if you had a Dexterity score of 0 (-5 modifier).
Size Modifier: Smaller creatures are harder to hit than bigger ones. Apply the appropriate Size Modifier to your Reflex Defense (And only your Reflex Defense). Size Modifiers are as follows: Colossal, -10; Gargantuan, -5; Huge, -2; Large, -1; Medium, +0; Small, +1; Tiny, +2; Diminutive, +5; Fine, +10.
Fortitude Defense
Your Fortitude Defense (Abbreviated Fortitude) represents your ability to resist the effects of Poison, Disease, and Radiation, as well as your ability to ignore effects that would incapacitate a normal being.
Heroic Level: Your Heroic Level is the sum of all levels you have in Heroic Classes (Jedi, Noble, Scoundrel, Scout, Soldier, Technician, and Force Prodigy) and Prestige Classes (Such as Ace Pilot or Sith Lord). It does not include levels in the Nonheroic class or Beast class.
Constitution Modifier: Tougher, healthier targets are more difficult to hurt than weaker ones, so you add your Constitution Modifier to your Fortitude Defense. A nonliving target (That is, any target without a Constitution score, such as a Droid) instead adds it's Strength Modifier to it's Fortitude Defense.
Equipment Bonus: Some kinds of Armor provide an Equipment Bonus to your Fortitude Defense.
Will Defense
Your Will Defense (Abbreviated Will) represents your willpower and your ability to resist certain Force Powers and other effects that attack your mind.
Heroic Level: Your Heroic Level is the sum of all levels you have in Heroic Classes (Jedi, Noble, Scoundrel, Scout, Soldier, Technician, and Force Prodigy) and Prestige Classes (Such as Ace Pilot or Sith Lord). It does not include levels in the Nonheroic class or Beast class.
Wisdom Modifier: Strong-willed characters are harder to influence than weak-willed ones. You add your Wisdom Modifier to your Will Defense. When you are unconscious, you have an effective Wisdom score of 0 (-5 modifier).