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Standard US Ring Sizes

USDIAMETER IN INCHESDIAMETER IN MM
0000
0.390

9.91

00
0.422

10.72

0
0.454

11.53

1/2
0.474

11.95

3/4
0.482

12.18

1
0.487

12.37

1 1/4
0.496

12.60

1 1/2
0.503

12.78

1 3/4
0.511

13.00

2
0.520

13.21

2 1/4
0.528

13.41

2 1/2
0.536

13.61

2 3/4
0.544

13.83

3
0.553

14.05

3 1/4
0.561

14.25

3 1/2
0.569

14.45

3 3/4
0.577

14.65

4
0.585

14.86

4 1/4
0.592

15.04

4 1/2
0.601

15.27

4 3/4
0.611

15.53

5
0.618

15.70

5 1/4
0.626

15.90

5 1/2
0.634

16.10

5 3/4
0.642

16.30

6
0.650

16.51

6 1/4
0.658

16.71
USDIAMETER IN INCHESDIAMETER IN MM
6 1/2
0.666

16.92

6 3/4
0.674

17.13

7
0.683

17.35

7 1/4
0.687

17.45

7 1/2
0.699

17.75

7 3/4
0.707

17.97

8
0.716

18.19

8 1/4
0.722

18.35

8 1/2
0.732

18.53

8 3/4
0.736

18.69

9
0.748

18.89

9 1/4
0.757

19.22

9 1/2
0.764

19.41

9 3/4
0.772

19.62

10
0.781

19.84

10 1/4
0.788

20.02

10 1/2
0.797

20.20

10 3/4
0.805

20.44

11
0.814

20.68

11 1/4
0.821

20.85

11 1/2
0.830

21.08

11 3/4
0.836

21.24

12
0.846

21.49

12 1/4
0.854

21.69

12 1/2
0.862

21.89

12 3/4
0.870

22.10

13
0.879

22.33