I'm afraid I can't help re: American sizing, as the conversions seem to vary, but Repetto are generally on the small side, so I would recommend going up half a size in most styles. Their ballerinas are cut fairly wide, but are quite shallow on the toe if that helps (I work in a shop that sells them, so I've tried on most styles and seen how they fit a variety of people). They're also very quick to mould to your feet- I bought my Jackie ballerinas slightly tight and they've stretched to fit me perfectly now. I adore mine though, they're the best fit I've ever tried in ballet pumps and are incredibly soft and comfortable. I only wish I hadn't had them rubber soled, they've lost a bit of their flexibility that way, even if it does make them harder wearing.