Size Chart Coats and Shirts:    Use measurements (A) and (C). Measure the length of pet's back from the base of the neck to the base of the tail, (A), and measure girth around broadest part of chest,(C). Collars:   Use measurement (B). Measure the circumference of the neck. Lifevests:    Use measurement (B),(C) and (D).Measure the circumference of the neck, (B). Measure girth around broadest part of chest, (C),and around waist (D). Kari-Pet�: Use measurements (A),(C) and Weight.Measure the length of pet's back from the base of the neck to the base of the tail, (A), and measure girth around broadest part of chest,(C). Due to the various sizes of pets within their own breed,it will help us to fill your order correctly, if you would use the above chart relating to the products you are purchasing.If you need help please call our toll free number and our staff will be glad to assist you. Otherwise, please refer to our  Contact Us  page for any questions or comments you might have. Thank-You Contact Pet Tags Plus  Today -- We are standing by to take your order. Pet Tags Plus Business Cell Phone: (731) 676-9010 tagstn@gmail.com