US Standard (Also  Canada) Diameter in Inches British Equivalent French Equivalent German Equivalent Swiss Equivalent Japanese Equivalent
0 .454 – – – – –
1/2 – A – – – –
1 .487 B – – – 1
1 1/2 .503 C – – – –
2 .520 D 41 ½ 13 ¼ 1 ½ 2
2 1/2 .536 E 42 ¾ 13 ¾ 2 ¾ 3
3 .553 F 44 14 4 4
3 3/8 – G 45 ½ – 5 ½ 5
3 1/2 .569 – – 14 ½ – –
3 3/4 – H 46 ½ – 6 ½ –
4 .585 H ½ – 15 – 7
4 1/4 – I 47 ¾ – 7 ¾ –
4 7/8 – J 49 – 9 –
5 .618 J ½ – 15 ¾ – 9
5 1/8 – K 50 – 10 –
5 1/2 .634 L 51 ¾ 16 11 ¾ –
6 .650 M 52 ¾ 16 ½ 12 ¾ 12
6 1/2 .666 N 54 17 14 13
7 .683 O 55 ¼ 17 ¼ 15 ¼ 14
7 1/4 .699 P 56 ½ 17 ¾ 16 ½ 15
8 .716 Q 57 ¾ 18 17 ¾ 16
8 1/2 .732 – – 18 ½ – 17
8 5/8 – R 59 – 19 –
9 .748 – – 19 – 18
9 1/8 – S 60 ¼ – 20 ¼ –
9 1/4 .764 – – 19 ½ – 19
9 5/8 – T 61 ½ – 21 ½ –
10 .781 T ½ – 20 – 20
10 1/4 – U 62 ¾ – 22 ¾ 21
10 1/2 .797 U ½ – 20 ¼ – 22
10 5/8 – V 63 ¾ – 23 ¾ –
11 .814 V ½ – 20 ¾ – 23
11 1/8 – W 65 – 25 –
11 1/2 .830 – – 21 – 24
11 5/8 – X 66 ¼ – 26 ¼ –
12 .846 Y 67 ½ 21 ¼ 27 ½ 25
12 1/2 .862 Z 68 ¾ 21 ¾ 28 ¾ 26
13 .879 – – 22 – 27

Ring Size Comparison Chart

Compliments of The International Gem Society