A: Hi Meredith! The manufacturer has a size chart on the packaging. The recommended measurements are as follows: Size Small- Neck to Tail: 11" Chest: 14" (Recommended for Chihuahua, Pomeranian, Australian Terrier, Yorkshire Terrier, Toy Poodle Size Medium- Neck to Tail: 15" Chest: 17" (Recommended for Pug, Maltese, Jack Russel Terrier, French Bulldog, Boston Terrier) Size Large- Neck to Tail: 22" Chest: 20" (Recommended for Bichon Frise, Beagle, Cocker Spaniel, Corgi, Scottish Terrier Thanks for your question!