Dog harness sizing chart | PetSmart Dog Harness Sizing Chart. Use the measurements below to help you choose the right harness. (1 lb = kg) Girth is measured by the widest part of your dog's chest. XX SMALL (Up to 5 lbs.) Common Breeds: Chihuahua & Teacup Yorkshire Terrier. GIRTH: 8 - 10" RECOMMENDED LEASH: 5/16" width. X SMALL (5-10 lbs.) Amazon: dog harness size chart Amazon's Choice for dog harness size chart. Chai's Choice Best Outdoor Adventure Dog Harness. 3M Reflective Vest with Two Leash Attachments. Caution - Please Measure Dog Before Ordering! Matching Leash and Collar Available. 4.4 out of 5 stars 4,558. $25 $ 25. 95. Get it as soon as Fri, Jul 26.