Let your outdoor dog, "pull his own weight," with this easy-on/easy-off Kyjen Outward Hound Excursion Backpack. When walking around town or hiking on the trail, this pack provides maximum comfort and convenience for your dog. Small for dogs < 18 lbs with 19-24" girth. Medium for dogs 18-50 lbs with a 26-32" girth. Large for dogs 50-79 lbs with a 30-40" girth. X-Large for dogs 80 lbs + with a 36-48" girth. (measured around the widest part of the dogs rib cage)