The best way to figure it out is visiting local jeweller or any jewelry store. Professional will help you better than any home method! Here at LOVEDEN Jewelry we use US size standards and you can use this trustworthy conversion chart in case if you got different standards measurements. 

 

Diameter
(mm)

Circumference
(mm)

United States
 & Canada

Australia,UK & Ireland

Euro PE

Spain & Italy

Japan

14.1

44.3

3

F

44

4

4

14.5

45.6

3.5

G

45

5.5

6

14.9

46.8

4

H

47

7

7

15.3

48.1

4.5

l

48

9

8

15.7

49.3

5

J 1/2

50

10

9

16.1

50.6

5.5

K 1/2

52

12

10

16.5

51.9

6

L 1/2

53

13

11

16.7

52.5

12

16.9

53.1

6.5

M 1/2

54

14

13

17.3

54.4

7

N 1/2

55

15

14

17.7

55.6

7.5

O 1/2

56

16.5

15

18.1

56.9

8

P 1/2

57

18

16

18.5

58.1

8.5

Q 1/2

58

19

17

18.8

59.1

18

19

59.7

9

R 1/2

59

20

19.4

61

9.5

S 1/2

60

21.5

19

19.8

62.2

10

T 1/2

61

22

20

20

62.9

21

20.2

63.5

10.5

U 1/2

62

23.5

22

20.6

64.7

11

V 1/2

63

25

23

21

66.0

11.5

W 1/2

64

26

24

21.4

67.2

12

X 1/2

66

27.5

21.5

67.6

25

21.6

67.9

68

21.8

68.5

12.5

Z

28

21.9

68.8

69

26

22.1

69.5

29

22.3

70.1

13

70

30

27

22.5

70.7

Z 1/2

22.6

71

13.5

22.7

71.3

71

31

28

22.9

72

Z+2

72

32

23.2

72.9

14

Z+3

23.4

73.5

Z+4