Country Brook Design | Rainbow Stripes Martingale Dog Collar-M Collar fits 15in - 21in size neck. There are no standard sizes for dog collars. Please be sure to measure your dog's neck for correct size. Measure around your dog's neck (with string or tape measure) snugly where you want the collar to lay. If you have any questions or problems with sizes please give us a call before ordering. 256-974-0700 Breed Recommendation: Greyhound, French Bulldog, or Collie Made in U.S.A. with top quality hardware Traditional martingale collar has no buckle for superior strength.