Sizes - Adjustable Range of Holes
(measured from base of buckle tongue)

Mini - 9-13" (Toy Poodle, Maltese, Jack Russell, Mini Dachshund)
Compact - 13-16-1/2" (Small Kelpie, Standard Dachshund, Corgi, Whippet, Springer Spaniel)
Coupe - 16-19-1/2" (Border Collie, Small Labradors, Malinois, Australian Shepherd)
SUV - 19-22-3/4" (Larger Labradors, Golden Retrievers, Bulldog, Rhodesian Ridgeback, Catahoula)

Be sure to measure your dog's actual neck, not his current collar to determine the best size. This can be done using a piece of string and then laying that against a tape measure or ruler.