We measure your arch. We don't guess it.
There's an Aetrex Albert 3D scanner in our Matthews store. You stand on it in bare feet for about twenty seconds and it measures both feet separately, to within a millimeter: length, width, girth, instep height and arch height.
That matters because Aetrex sort their orthotics by arch height and forefoot pressure, not by shoe size. This one is their Fit B. A scan tells us whether that's you, or whether you want a different shape entirely, and most people find their two feet don't give the same answer.
It's free, and you're under no obligation to buy anything from it.