Shoe size is particular tricky as you are dealing with a three-dimensional object. It's not only the length and width which makes a shoe fitting or not, but also the toe shape and the height of the instep. Even from the same maker, different lasts can fit differently. As far as the length is concerned, there is about Â½ size difference between English and American sizes, but in my opinion, the different toe shapes negates that to quite an extend. Most American shoes have a rounder toe shape, while English shoe are more almond shaped. With some shoes I take the same size in American and English. English shoes are also higher in the instep than their American cousins. An American D will be much shallower than an English E or F, although the width might be similar. If you want to buy shoes by mail order and you have no opportunity to try them on, be very specific what fits you: Not simply American 9 Â½ D but Alden "Aberdeen" 9 Â½ D (which is completely different from Alden "Barry" 9 Â½D). Mail order merchants will be pretty aware how different makers sizes run. Make sure you can return them if the size is not right. Try an English size 9 E or F to begin with, but if you were measured for Allen-Edmonds, 9 Â½ E probably would be the better size. P.S. My "normal" shoe size is about 8 Â½, but I have shoes between 7 (Prada's sizing is freakish) and 9 Â½ Â (Brooks Brothers' Bucks).