Board Thread:Dark Souls II/@comment-5150818-20140316020250/@comment-5264386-20140316031038

You also have to have 1.5 times the Strength and Dexterity requirements of both weapons to enter the Power Stance (although, if one has higher requirements than the other, it'll probably work out 1.5 time the higher weapon's requirements).

For instance, let's assume that all weapons are compatibile with each other, and say I had the Heide Knight Sword in my right hand, and the Zwiehander in my left. I'd thus need 36 Strength and 18 Dexterity to enter the Power Stance, since 24 x 1.5 = 36, and 12 x 1.5 = 18.