First, I would not buy this shoe again.  I thought I would try it because it was half price and I have worn Clark's before with no problem.  I have always worn a medium shoe.  This medium shoe is not only narrow in width, but the vertical toe room is not as deep was most other brands of walking shoes I have tried.  I cannot wear my normal thick socks with these which is a pain because I walk a lot.  I normally wear a 5.5 medium, but because of other reviews, I ordered a 6M.  I could not have worn a 5.5.  If you plan to order this shoe, I would recommend you find it in a store to determine your correct size before you order.  It is just not a comfortable shoe for me.