The SENSE-ible Dog Harness is an easy to use no-pull dog harness. The front-leash attachment design gently stops dogs from pulling, without causing stress or strain on your dog's neck. Sizing For the SENSE-ible Harness: Using a flexible measuring tape (or leash), measure from just behind the front legs all the way around your dog, similar to a chest or belt measurement on a human. This is your dog's girth measurement. X-Small: 3/8 Inch Webbing (16.5-20.5" girth). Small: 5/8 Inch Webbing (20-24.5" girth). Medium: 3/4 Inch Webbing (24-28" girth). Med/Large: 3/4 Inch Webbing (26-32" girth). Medium/Large: 1 Inch Webbing (27-32.5" girth). Large: 3/4 Inch Webbing (32-40" girth). Large: 1 Inch Webbing (32-40" girth). X-Large: 1 Inch Webbing (39-50" girth).