Our ring size is a US 6.5 with an open back, by default.We do not recommend adjusting the ring by yourself (moving the open back).If you have a different size, please write it in the order notes or write us an email ASAP.You may choose two different sizes which refer to the size of the centerpiece (the map itself).Large ring: The centerpiece measures: 1.5in / 38mmSmall ring: The centerpiece measures: 1in / 28mm