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Value in inches

Ring Size Equivalents

MM to Inch
Conversion Table
mm approx. inches
1mm 1/32"
2mm 1/16"
3mm 3/32"
4mm 1/8"
5mm 3/16"
6mm Just under 1/4"
7mm Just over 1/4"
8mm 5/16"
9mm Just under 3/8"
10mm Just over 3/8"
11mm 7/16"
12mm Just under 1/2"
13mm Just over 1/2"
14mm 9/16"
15mm Just under 5/8"
16mm  5/8"
17mm Just under 11/16"
18mm Just under 3/4"
19mm Just over 3/4"
20mm Just under 13/16"
21mm Just over 13/16"
22mm Just under 7/8"
23mm Just over 7/8"
24mm 15/16"
25mm 1"
 
Ring Size Equivalents
U.S. &
Canada
Inside
Diameter
Inside
Circumference
Great
Britain
France Germany Japan Switzerland
3-1/2 ... ... ... ... 14-1/2 ... ...
3-3/4 ... ... H 46-1/2 ... 6-1/2 6-1/2
4 16 mm 50 mm H-1/2 ... 15 7 ...
4-1/4 ... ... I 47-3/4 ... ... 7-3/4
4-1/2 ... ... I-1/2 ... 15-1/4 8 ...
4-3/4 ...   J 49 ... ... 9
5 17 mm 53 mm J-1/2 ... 15-3/4 9 ...
5-1/4 ... ... K 50 ... ... 10
5-1/2 ... ... L 51-3/4 16 ... 11-3/4
5-3/4 ... ... L-1/2 ... ... 11 ...
6 17.5 mm 55 mm M 52-3/4 16-1/2 12 12-3/4
6-1/2 ... ... N 54 17 13 14
7 18 mm 57 mm O 55-1/4 17-1/4 14 15-1/4
7-1/2 ... ... P 56-1/2 17-3/4 15 16-1/2
8 19 mm 60 mm Q 57-3/4 18 16 17-3/4
8-1/2 ... ... ... ... 18-1/2 17 ...
8-3/4 ... ... R 59 ... ... 19
9 20 mm 63 mm ... ... 19 18 ...
9-1/4 ... ... S 60-1/4 ... ... 20-1/4
9-1/2 ... ... ... ... 19-1/2 19 ...
9-3/4 ... ... T 61-1/2 ... ... 21-1/2
10 21 mm 66 mm T-1/2 ... 20 20 ...
10-1/4 ... ... U 62-3/4 ... 21 22-3/4
10-1/2 ... ... U-1/2 ... 20-1/4 22 ...
10-3/4 ... ... V 63-3/4 ... ... 23-3/4
11 21.5 mm 68 mm V-1/2 ... 20-3/4 23 ...
11-1/4 ... ... W 65 ... ... 25
11-1/2 ... ... ... ... 21 24 ...
11-3/4 ... ... X 66-1/4 ... ... 26-1/4
12 22.5 mm 71 mm Y 67-1/2 21-1/4 25 27-1/2
12-1/2 ... ... Z 68-3/4 21-3/4 26 28-3/4
13 23 mm 73 mm ... ... 22 27 ...