My baby fit in his newborn-3 sized Gap clothes until 11 ish pounds. That's with cloth diapers which are a bit bulkier.
Every other "newborn" brand he was out of around 8lbs. Now, I don't know if Gap has just newborn sized, but all of mine say newborn to 3 months or something like that. They were actually too big on him at first when he was in the 6lbs range.