Measure the internal diameter of a rign that fits you (The best way to do that is if you use a gauge). Compare the result with the data in the table below so you can choose the right size.

Europe Bulgaria
size circumference (mm) diameter (mm)
5 45 14.0
6 46 14.3
7 47 14.6
8 48 15.0
9 49 15.3
10 50 15.6
11 51 16.0
12 52 16.3
13 53 16.6
14 54 17.0
15 55 17.3
16 56 17.6
17 57 18.0
18 58 18.3
19 59 18.6
20 60 19.0
21 61 19.3
22 62 19.6
23 63 20.0
24 64 20.3
25 65 20.6
26 66 21.0
27 67 21.3
28 68 21.6
29 69 22.0
30 70 22.3
31 71 22.6
32 72 23.0
33 73 23.3
34 74 23.6