Recommended for Small Medium Dogs: This pet carrier backpack is designed for carrying small dogs and puppies, S is for dogs weighing less than 10 Pounds, M for dogs less than 18 Pounds, L for < 26 Pounds, XL for < 30 Pounds. Please MEASURE before buying, choose accordingly from our size chart, prioritizing BACK LENGTH when between sizes. DO NOT choose size based on dog breeds or dog's usual size Adjustable Safety Straps Design: This safety straps can make sure your puppy 100% secured in the dog carrying backpack, when attached it to your dog’s collar About Size: Please measure BACK LENGTH and CHEST GIRTH accordingly before purchasing, the BACK LENGTH is mean from the end of neck to the start of the tail (Not include the tail), If between sizes, please PRIORITIZE BACK LENGTH. If you have any questions, please ask us first 2 Ways of Wearing for Outdoor: The hands-free backpack for dogs can be worn on your front side or your backside if you love, Provides you and your dogs with comfort ways to travel including cycling, motorcycling, walking, hiking, camping Better Breathability and comfortable: The more open area and all the air mesh padding on this puppy backpack ensures breathability, keeping you and your pet from being stuffy and allowing your pet to move more freely without being restrained PetBonus Pet Dog Carrier Backpack -- Make Your Adventures with Your Pet Easier! PetBonus committed to provide you and your pet a better way to enjoy your life. And exploring the outside world is our pet's eternal motivation. To meet your summer vocation need, we upgraded our dog backpack carrier, made it more comfortable and breathable and ensured you and your pet's comfort at the same time. Notice:1. Recommended for Medium Small Dogs under 35 pounds.2. Each dog is unique. Please measure before purchasing. (size chart is in main pic #5) 3. The measurement data might be a slight deviation due to manual measurements. Broader Shoulder Straps, Less Pain to yourself 1. To eliminate the pain on our shoulders after a prolonged use, we widen thicken the shoulder straps on this dog carrying backpack. 2. To make the carrying process more comfortable for us, there are 2 adjustable fasten buckles on the back and waist, which distributes the weight evenly across the shoulders, back and waist. Simplified Wearing Process, Reduced Wearing Pain 1. Much bigger limb holes make the wearing process easier and faster. Instead of being restricted by the small and tight limb holes, these open areas give their free limbs back. 2. All buckles design on our dog front carrier avoids our pets from getting caught by zippers when wearing it or zipper slippages while carrying it. No Choking Hazard, Better Chest Support 1. We redefine the neck design of this dog chest carrier by removing the elastic band and cutting it into V-shape. It will no more restrain the pet's neck and causing the possible choking hazard. 2. To support our pet to seat still, we used thicken pearl cotton to do the job. Not only does it do the job perfectly, it also maximizes the comfort of our pets safely.