A. Back: Measure length of pet’s back from the base of the neck to the base of the tail. See below for estimating by breed.
B. Neck: Measure the circumference of the pet’s neck for a snug, not tight fit. No need to add inches as you would with a collar.
C. Chest/Girth; Measure the broadest part of the chest and add 2".

Note: If the dog has a stout build, select one size larger.

Recommended sizing by breed (for approximation only):

XX-Small: Teacup and dogs under 5 lbs
X-Small: Australian Terrier, Chihuahua, Pomeranian, Toy Poodle, Yorkshire Terrier
Small: Boston Terrier, Jack Russell Terrier, Maltese, Pug, Silky Terrier
Medium: Bichon Frise, Beagle, Cocker Spaniel, Corgi, Scottish Terrier
Large: Brittany Spaniel, Bulldog, Collie, Schnauzer, Springer Spaniel
X-Large: Doberman Pinscher, German Shepherd, Golden Retriever, Labrador Retriever, Rottweiler
XX-Large: Irish Wolfhound, Great Dane, Mastiff, Newfoundland, St. Bernard