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.
Neck: Measure the circumference of pet's neck for a snug fit. No need to add inches as you would with a collar.
Chest/Girth: Measure girth around 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:
Teacup: Dogs under 5 lbs
XX-Small: Chihuahua, Chinese Crested, Pomeranian, Toy Poodle
X-Small: Brussels Griffon, English Toy Spaniel, Maltese, Miniature Dachshund, Norfolk Terrier, Papillon, Yorkshire Terrier
Small: Austrialian Terrier, Border Terrier, Boston Terrier, French Bulldog, Miniature Pinscher, Miniature Poodle, Pekingnese, Pug, Shih Tzu, Silky Terrier, West Highland Terrier
Medium: Beagle, Bichon Frise, Brittany Spaniel, Cairn Terrier, Cocker Spaniel, Corgi, Jack Russell Terrier, Lhasa Apso, Scottish Terrier