International Ring Size Conversion Table

US  & Canada Diameter
(inch)		 Diameter
(mm)		 Metric
(mm)		 British  French  German  Japanese  Swiss 
0 0.39 9.91   -        
00 0.422 10.72   -        
000 0.454 11.53   -        
1/4 0.474 11.95   A        
3/4 0.482 12.18   A 1/2        
1 0.487 12.37 38.9 B     1  
1 1/4 - 12.6 39.6 B 1/2        
1 1/2 0.503 12.78 40.2 C        
1 3/4 - 13 40.8 C 1/2        
2 0.52 13.21 41.5 D 41 1/2 13 1/2 2 1 1/2
2 1/4 - 13.41 42.1 D 1/2 - -    
2 1/2 0.536 13.61 42.7 E 42 3/4 13 3/4 3 2 3/4
2 3/4 - 13.83 43.4 E 1/2 - -    
3 0.553 14.05 44 F 44 14 4 4
3 1/8 - 14.15 44.3 F 1/2 - -    
3 1/4 - 14.25 44.6 - - -    
3 3/8 - 14.36 44.9 G 45 1/4 - 5 5 1/4
3 1/2 0.569 14.45 45.2 - - 14 1/2    
3 5/8 - 14.56 45.6  G 1/2 -   6  
3 3/4 - 14.65 45.9 H 46 1/2     6 1/2
4 0.585 14.86 46.5 H 1/2 - 15 7  
4 1/4 - 15.04 47.1 I  47 3/4     7 3/4
4 1/2 0.601 15.27 47.8 I 1/2 - 15 1/4 8  
4 5/8 - 15.4 48.1 J 49 15 1/2   9
4 3/4 - 15.53 48.4 - -      
5 0.618 15.7 49 J 1/2 - 15 3/4 9  
5 1/8 - 15.8 49.3 K 50     10
5 1/4 - 15.9 49.6 - -      
5 3/8 - 16 50 K 1/2 -   10  
5 1/2 0.634 16.1 50.3 L 51 3/4 16   11 3/4
5 3/4 - 16.3 50.9 - -      
5 7/8 - 16.41 51.3 L 1/2 -      
6 0.65 16.51 51.5 M 52 3/4 16 1/2 12 12 3/4
6 1/4 - 16.71 52.2 M 1/2 -      
6 1/2 0.666 16.92 52.8 N 54 17 13 14
6 3/4 - 17.13 53.4 N 1/2 -      
7 0.683 17.35 54 O 55 1/4 17 1/4 14 15 1/4
7 1/4 - 17.45 54.7 O 1/2 -      
7 1/2 0.699 17.75 55.3 P 56 1/2 17 3/4 15 16 1/2
7 3/4 - 17.97 55.9 P 1/2 -      
8 0.716 18.19 56.6 Q 57 3/4 18 16 17 3/4
8 1/4 - 18.35 57.2 Q 1/2 -      
8 1/2 0.732 18.53 57.8 - - 18 1/2 17  
8 5/8 - 18.61 58.4 R 59     19
8 3/4 - 18.69 58.4 - -      
8 7/8 - 18.8 59 R 1/2 -      
9 0.748 18.89 59.1 - - 19 18  
9 1/8 - 19.1 59.4 S 60 1/4     20 1/4
9 1/4 - 19.22 59.7 - -      
9 3/8 - 19.31 60 S 1/2 -      
9 1/2 0.764 19.41 60.3 - - 19 1/2 19  
9 5/8 - 19.51 60.6 T 61 1/2     21 1/2
9 3/4 - 19.62 60.9 - -      
10 0.781 19.84 61.6 T 1/2 - 20 20  
10 1/4 - 20.02 62.2 U 62 3/4   21 22 3/4
10 1/2 0.797 20.2 62.8 U 1/2 - 20 1/4 22  
10 5/8 - 20.32 63.1 V 63     23 3/4
10 3/4 - 20.44 63.5 - -      
11 0.814 20.68 64.1 V 1/2 - 20 3/4 23  
11 1/8 - 20.76 64.3 W 65     25
11 1/4 - 20.85 64.7 - -      
11 3/8 - 20.94 65 W 1/2 -      
11 1/2 - 21.08 65.3 - - 21 24  
11 5/8 0.83 21.18 65.7 X 66 1/4     26 1/4
11 3/4 - 21.24 66 - -      
11 7/8 - 21.3 66.3 X 1/2 -      
12 0.846 21.49 66.6 Y 67 1/2 21 1/4 25 27 1/2
12 1/4 - 21.69 67.2 Y 1/2 -      
12 1/2 0.862 21.89 67.9 Z 68 3/4 21 3/4 26 28 3/4
12 3/4 - 22.1 68.5 Z 1/2 -      
13 0.879 22.33 69.1 - - 22 27