The NECK sizes below indicate the size of the dogs' neck. The WAIST sizes indicate the dogs' chest, measured behind the front legs.
XS - 31-37 cm / 12.5-15in
Affenpinscher, Chihuaha, Australian Silky Terrier, Chinese Crested, Dachshund (Miniature), English Toy Terrier, Griffon Bruxellois, Italian Greyhound, Japanese Chin, King Charles Spaniel, Lowchen, Maltese, Papillon, Pekingese, Pinscher (Miniature) Pomeranian, Poodle (Toy), Yorkshire Terrier.
S - 38-56 cm / 15-22.5in
Basenji, Beagle, Bolognese, Bichon Frise, Dachshund, Finnish Spitz, Hungarian Puli, Italian Grey Hound, Lhasa Apso, Norwegian Buhund, Poodle (Miniature), Schipperke, Schnauzer (Miniature), Shetland Sheepdog, Shihtzu, Spaniel (American Cocker, Cocker, Brittany, Cavalier King Charles, Cocker), Terrier (American, Australian, Bedlington, Border, Boston, Bull-miniature, Cairn, Dandie Dinmont, Fox, Irish, Kerry Blue, Lakeland, Manchester, Norfolk, Norwich, Scottish, Sealeyham, Skye, Staffordshire Bull, Tibetan, Welsh, West Highland Terrier), Welsh Corgi (Cardigan), Welsh Corgi (Pembroke).
M - 42-65 cm / 17-26in
Airedale Terrier, American Straffordshire, Australian Cattle Dog, Australian Kelpie, Azawakh, Basset Hound, Bearded Collie, Border Collie, British Bulldog, Bull Terrier (Standard), Char-Pei, Chow-Chow, Dalmation, Elkhound, Foxhound, German Shorthaired Pointer, Hungarian Vizsla, Keeshond, Ibizan, Italian Spinone, Large Munsterlander, Pharoah Hound, Pointer, Plott, Pointers, Poodle (Standard), Portuguese Water Dog, Redbone Coon Hound, Saluki, Samoyed, Schnauzer (Standard), Setter (English, Gordon, Irish), Siberian Husky, Sloughi, Soft Coated Wheaten, Spaniel (Clumber, Field, Irish Water, Springer, Welsh, Sussex), Stumpy Tail Cattle Dog, Vizsla, Whippet.
L - 58-78 cm / 23-31in
Afghan Hound, Akita, Alaskan Malamute, Belgian Sheepdog, Bouvier des Flandres, Briard, Borzoi, Bouviers des Flandres, Boxer, Chesapeake Bay Retriever, Chart Polski, Collie, Doberman, German Shepherd, German Wire haired Pointer, Grey Hound, Norwegian Elkhunfd, Old English Sheepdog, Rhodesian Ridgeback, Rotweiller, Schnauzer (Giant), Spaniel (Springer, English, Sussex-Large); Spanish Mastiff, Weimeraner.
If your dog's head, neck, and body are all approximately the same size (i.e. as with Pugs and similar breeds), a step-in harnesses is not suitable for your dog.