This photo shows an english saddle pictures from the front. The way this saddle is being measured is a somewhat effective method of measuring the width of a saddle you plan to list on ebay or sale online. It is always important to provide accurate measurements for saddles sold online, since some horses require a very specific size.
Before trying to measure the saddle’s width with this method, a better way to determine how wide the tree of a saddle is is to lift the flap on both sides and look for a buckle guard with a maker’s mark stamped on it. If you can find the flap of leather emblazoned with the manufacturer’s name or the model name, there is often a number stamped in a discrete corner of that piece of leather. The number should range from 27-33, with the vast majority of saddles falling in the 30-32 range (31 being “average”)