run small! Small compared to Allen Edmonds. In a cap I comfortably wear 10.5 d. So I got 10.5d with this loafer. It's definitely too small. At least half a size. I don't understand why but it's true. Haven't returned them for a different size yet, but I would recommend going half a size up from your usual Allen Edmonds sock size, but going half a size up may not be enough. I think it will. Hope that helps.