There are calculators online that can help you get an estimate as to how big he'll be. Just google 'puppy weight calculator' and one should pop up.
If you tell us his weight someone here can probably give you an estimate - but without knowing his breed exactly it's just an estimate, not a certainty.
He's very cute. He's too young to tell what breed he may be - but also keep in mind he could just be pure pitbull. Just because the mother escaped doesn't mean she didn't cross paths with another pit. He does look like a pit x shepherd pup I rescued, but again, he's too young to really tell. He kinda just looks like a pit puppy too. Puppies just look like puppies until they get a bit older - even then you can't always tell.