How big of prey?

I have a dwarf boa. He is about 3 ft long but about 1" from top to bottom. Can he eat a med/large rat? If I lay the rat out she is not bigger then the widest part of his body, but he has a WIDE body for his size (bigger than what I am used to for balls and corns). I don't want to over feed him. Can anyone help? Thanks

A full body picture to get an idea of exactly how wide he is in comparison to his length would be helpful. If he already seems fatter overall than any bps you're used to seeing then he may be overweight to begin with. Boas, at least the ones I've had experience with, tend to be a bit slimmer in comparison to bps or other bulky bodied snakes.
I usually see the recommendation of feeding a prey item that is the same width as the widest part of the snake, but in your case if it is determined that it seems a bit girthy for it's length then it may be a good idea to feed it something slightly smaller.
Then again, it may just be one of those that looks a bit fatter than the norm.