The Back Length is one of the hardest measurements to get and it is very difficult to do if your dog is wiggly and won’t stand up still and straight. You will need two people to obtain an accurate measurement because the dog cannot be turning, sitting, or slouched. Your dog must be standing straight with the head up. Start at the base of the neck (feel for the shoulder blades at the withers, measure from just in front of the shoulder blades) to the base of the tail (rump, not over the tail).
Back length is just a general estimate and should be the last thing we consider when looking at sizes. Because different breeds will have different shoulder and tail placements it is impossible to get a ‘one size fits all’ sizing based on back length alone. Back Length should be used to help differentiater between Standard and Long & Lean sizes after all other measurements are considered.