NACOCO Pet Leash Dog Navy Vest Harnesses Size X-small: Neck girth 7.9 inches, Chest girth 10.2 inches Size Small: Neck girth 12.6 inches, Chest girth 12.6 inches Size Medium: Neck girth 10.2 inches, Chest girth 14.2 inches Size Large: Neck girth 12.6 inches, Chest girth 17.3 inches Size X-Large: Neck girth 15 inches Chest girth 19.7 inches