All Herm Sprenger pinch collars come in a standard length which is adjusted to fit the neck of the dog by removing or adding links to the collar. The size of this particular pinch collar is 23 inches (58 cm) with prong's diameter - 1/8 inches (3.2 mm). So, it will do for dogs with 21 inches (53 cm) neck size. If your dog's neck circumference is more than 21 inches (53 cm), you can order additional links. Each will add 1 1/2 inches (4.2 cm) to the total collar length. Go to the tab “YOU MAY ALSO WANT” to learn more about extra links for this prong collar.