Ring Sizes by Country  Measurement Data(MM)
US Germany Japan Switzerland UK Perimeter Diameter
5 15.75 9 49 J1/2 49.3 15.7
6 16.50 12 51.5 I1/2 51.8 16.5
7 17.25 14 54 0 54.4 17.3
8 18 16 56.5 Q 56.5 18.1
9 19 18 59 S 59.5 18.9
10 20 20 61.5 T1/2 62.1 19.8
11 20.75 23 64 V1/2 64.6 20
12 21.25 25 66.5 Y1/2 67.2 21.4

NOTE: This chart provides general sizing information, which can vary depending on style. Still unsure about your ring size?