LENGTH - The length of your dog's back, measured along the top of the spine from between the shoulders to the base of the tail.​NECK - This measurement is taken all the way around the neck at the place where your dog's collar would naturally rest.​CHEST - This measurement is taken all the way around the biggest part of your dog's ribcage, just behind the front legs. If you would like further advice in choosing the right sized product for your dog then please contact info@blanctofu.com