You can wield single-handed weapons in one hand if they are 1/2
to 4/3 of your size, or in two hands if they are up to three
times your size. The exception to this rule is the fellblade,
since the "bladesizing" spell only allows to resize it to up to
twice your size. Two-handed weapons can only be wielded in two
hands and need to be 1/2 to 4/3 of your size.
    
    Single-handed weapons are ancients, axes, bludgeons, broad
blades, daggers, held items, nets, thin blades, weapon breakers
and whips.

    Two-handed weapons are polearms, staffs, garrotes and all
ranged  weapons. 

    Shields are treated like heavy armor and can be wielded if the
shield is less than 10% larger than your size or if your size is
less than 10% larger than the shield.
    
    See Also: HELP SIZE, HELP WEAPONS