I will be getting a digital scale tomorrow and I will know exactly, but I did pick up some small mice before I realized that we may be able to order the rats. The mice are probably 3/4 of his largest width. I have never seen a rat put to compare in size and it did seem when I offered it last night that he wasn't too sure how to grab and swallow it. He doesn't seem to like to strike and is more interested in just slithering up to it and grabbing it with his mouth. How long do they usually stay on one food size while they are growing?