15.2 ct Authentic Amethyst Sterling Silver Party Ring

This item was made by genuine 925 sterling silver and set with a 15 mm (approx 15.2 ct) authentic natural amethyst. the ring top width is approx 21 mm and the bottom ring band thickness is approx 7 mm.    What standard are those ring sizes listed above? 1. All our store ring sizes are in US standard. 2. If you are not sure about your US size, kindly refer to the page of "Ring Size Table"at the bottom of the page, please.