Hola Duncan,In looking into a few possible options and tools, you are correct where having the option of the length/width return for a existing polygon, does not seem to be a current option or a tool. I was able to locate a few tools but they also determine the length/width but for a new polygon ad not a existing one. If this is a option you are looking to have, please post this on our Ideas site and look to have other promote it. Gracias, Duncan!ArcGIS Ideashttp://ideas.arcgis.com/