S - Tape width: 11mm and chest circumference: 200-310mm. Ideal for small breeds such as Chihuahua, Malts or Yorkshire. M - Tape width: 16mm and chest circumference: 260-400mm. Ideal for small-medium breeds such as Jack Russell, Terrier or Pug. L - Tape width: 20mm and thoracic perimeter: 340-560mm. Ideal for medium-large breeds such as Spaniel, Dalmatian or Boxer. XL - Tape width: 25 mm and thoracic perimeter: 430-700mm. Ideal for large breeds such as Labrador, Rottweiler or Dogo.