Every shoe is different. You need to try on lots of different kinds. I have wide, duck feet and Sidi's generally don't fit -- but the cheapest Sidi's ($100) fit like a charm because they have velcro over the ball and the instep - so they can be adjusted. I wear a size 7 American & approx 37 Euro. But, it can be a 36 or a 38, depending on the shoe.