It is important to note that the back length is the most important measurement of the three. The Chillybuddy Cooling Jacket provides room for adjustment in the girth and neck straps so it is crucial that the Chillybuddy Cooling Jacket you get covers the length of your dog's back. When in doubt, a little excess on the back length is better than having it be too short. If you have measured your dog and still have questions, please don't hesitate to contact us at email@example.com . We want your Chillybuddy to fit your dog as well as possible!