There are 4 sizes of this backpack: S: 28cm x 18cm M: 32cm x 20cm L: 38cm x 23cm XL: 41cm x 25cm Recommended for 5LB Small Dog & Cat 15LB : Pawaboo dog carrier backpack is designed for carrying small dogs/cats, we highly recommend for puppies less than to 15 LB (The larger dog may bring too much weight-bearing for the owner). Please DO measure your pets and choose according to the size chart . Considerate Detail-oriented Design: Legs-out and tail-out design keep your pet safe and comfortable; Hook and loop, zipper and elastic openings allow you to fit your dog inside comfortably; Quick Release Buckles on the end of straps ensure quick installation with just one hand. Customer Experience Comes First: We always stand behind our customers and try best to meet your needs. We have made several upgraded improvements such as thickening shoulder pad sponge, using upgraded breathable mesh and polyester fiber material, which makes the carrier more durable and comfortable. Two Ways of Wearing: A hands-free pet carrier can be worn on your front side or your backside if you like, it keeps you closer and increases pet's sense of security when you carry your cat or dog around. Meanwhile, the thickened sponge pad helps to relieve the burden of your shoulder. Enjoy Trips with Your Pet: This backpack carrier is lightweight and portable, you can use it to carry small dogs or cats for biking, hiking, camping, out walking or meeting friends. It allows owners and their lovely pets to have more adventures together, what's more, it's also a great photo prop to take funny pictures for daily sharing.