Levi weighs 5.5 pounds and usually eats around 1/4 cup per day. He'd eat the entire bag if I let him, so we had to switch from free-feeding to measured feeding.
He gets 1/8 cup twice a day. I'll occasionally feed him closer to 1/4 cup, or I will feed him 1/8 cup three times a day, just depending on his activity level!
Good luck finding what works for your guys!