[PF]Oversized Weapons, BFS

[PlusSixPelican]

If a character were to wield an oversized weapon (for the sake of argument, a Large Gladius, Dagger, or other light blade for a Medium character), how would that work?

[Squirrel_Dude]

To quote the rules on weapon size.

Weapon Size[link] (http://paizo.com/pathfinderRPG/prd/equipment.html)
Every weapon has a size category. This designation indicates the size of the creature for which the weapon was designed.

A weapon's size category isn't the same as its size as an object. Instead, a weapon's size category is keyed to the size of the intended wielder. In general, a light weapon is an object two size categories smaller than the wielder, a one-handed weapon is an object one size category smaller than the wielder, and a two-handed weapon is an object of the same size category as the wielder.

Inappropriately Sized Weapons: A creature can't make optimum use of a weapon that isn't properly sized for it. A cumulative –2 penalty applies on attack rolls for each size category of difference between the size of its intended wielder and the size of its actual wielder. If the creature isn't proficient with the weapon, a –4 nonproficiency penalty also applies.

The measure of how much effort it takes to use a weapon (whether the weapon is designated as a light, one-handed, or two-handed weapon for a particular wielder) is altered by one step for each size category of difference between the wielder's size and the size of the creature for which the weapon was designed. For example, a Small creature would wield a Medium one-handed weapon as a two-handed weapon. If a weapon's designation would be changed to something other than light, one-handed, or two-handed by this alteration, the creature can't wield the weapon at all.

As for the specific question, a large gladius would cause a medium character to take a -2 to hit, and he would deal 1d8 damage, wielding it as a 1 handed weapon instead of as a light weapon. If the character was nonproficient with the gladius, it would be a -6 penalty to hit.