Updated Guardian Gear® Aquatic Pet Preservers to provide more safety than ever for water-loving dogs. New and improved features include: more flotation material, strong, non-restrictive straps with quick-lock clips at belly, and sturdy, tear-resistant fabrics. 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: 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 Size Fits Length Fits Neck Fits Chest XX-Small Up to 6" 7" - 9" 10" - 14" X-Small 6" - 8" 8" - 10" 14" - 19" Small 8" - 12" 10" - 12" 18" - 24" Medium 12" - 16" 12" - 18" 22" - 30" Large 16" - 20" 16" - 22" 26" - 34" X-Large 20" - 24" 22" - 28" 30" - 40" XX-Large 24" - 30" 26" - 30" 35" - 45"