Our dog weighs 20 lbs.an he fits in the large size just fine. We found the small size too small. It goes together easily and is good quality material. We flew Jet Blue and they required the dog to sit on my lap for the entre 31/2hr.flight even though I had to pay for the seat. The dog was fine with it and so was I. Returning home I checked the carrier and walked the dog onto the plane.