Typically clematis and other vines are only shown with a height estimation, never a width :-) That's because it is their nature to grow vertically, not horizontally. Generally, width is only established when you manually train the vining stems laterally and so that can be extremely variable. Even vines that are trained to grow horizontally like along the top of a fence are only listed as to a height - that horizontal growth is actually the length (height) of the vine trained sideways as opposed to vertically.