I'm a size 12 (AU) but normally go up for my bra size to a 14D. I purchased this bra in a medium and it fits well. The bra doesn't offer great bust support but is fine to wear under casual/holiday style tops and dresses with a thin strap in the hot weather as it doesn't dig in or pinch like a normal strapless bra. The good part about the underwire is that the soft bra doesn't slip down like the type without this feature and actually stays in place. it is very comfortable so I also purchased in black and beige.