Benefit: On your action, before making
attack rolls for a round, you may choose to subtract a number from all melee
attack rolls and add the same number to all melee
damage rolls. This number may not exceed your base
attack bonus. The penalty on attacks and bonus on
damage apply until your next turn.
Special: If you attack with a two-handed weapon, or with a one-handed weapon wielded in two hands, instead add twice the number subtracted from your
attack rolls. You can't add the bonus from Power Attack to the
damage dealt with a light weapon (except with unarmed strikes or natural weapon attacks), even though the penalty on
attack rolls still applies. (Normally, you treat a double weapon as a one-handed weapon and a light weapon. If you choose to use a double weapon like a two-handed weapon, attacking with only one end of it in a round, you treat it as a two-handed weapon.)