Diameter

Circumference

US/Canada

British

Japanese

Swiss

(mm)

(mm)

Standard

Irish

Australian

11.6

36.5

0

11.8

37.2

1/4

12.0

37.8

1/2

A

12.2

38.4

3/4

A 1/2

12.4

39.1

1

B

1

12.6

39.7

1 1/4

B 1/2

12.9

40.4

1 1/2

C

13.1

41.0

1 3/4

C 1/2

13.3

41.6

2

D

2

1.50

13.5

42.3

2 1/4

D 1/2

13.7

42.9

2 1/2

E

3

2.75

13.9

43.5

2 3/4

E 1/2

14.1

44.2

3

F

4

4.00

14.3

44.8

3 1/4

F 1/2

5

5.25

14.5

45.5

3 1/2

G

14.7

46.1

3 3/4

G 1/2

6

6.50

14.9

46.7

4

H 

7

15.1

47.4

4 1/4

H 1/2

7.75

15.3

48.0

4 1/2

I 

8

15.5

48.7

4 3/4

J

9.00

15.7

49.3

5

J 1/2

9

15.9

49.9

5 1/4

K

10.00

16.1

50.6

5 1/2

K 1/2

10

16.3

51.2

5 3/4

L

11.75

16.5

51.8

6

L 1/2

11

12.75

16.7

52.5

6 1/4

M 

12

16.9

53.1

6 1/2

M 1/2

13

14.00

17.1

53.8

6 3/4

N

17.3

54.4

7

N 1/2

14

15.25

17.5

55.0

7 1/4

O 

17.7

55.7

7 1/2

O 1/2

15

16.50

17.9

56.3

7 3/4

P 

18.1

56.9

8

P 1/2

16

17.75

18.3

57.6

8 1/4

Q 

18.5

58.2

8 1/2

Q 1/2

17

18.7

58.9

8 3/4

R

19

18.9

59.5

9

R 1/2

18

19.2

60.1

9 1/4

S

20.25

19.4

60.8

9 1/2

S 1/2

19

19.6

61.4

9 3/4

T

21.5

19.8

62.1

10

T 1/2

20

20.0

62.7

10 1/4

U

21

20.2

63.3

10 1/2

U 1/2

22

22.75

20.4

64.0

10 3/4

V

20.6

64.6

11

V 1/2

23

20.8

65.2

11 1/4

W

25

21.0

65.9

11 1/2

W 1/2

24

21.2

66.5

11 3/4

X

21.4

67.2

12

X 1/2

25

27.50

21.6

67.8

12 1/4

Y 

21.8

68.4

12 1/2

Z

26

28.75

22.0

69.1

12 3/4

Z 1/2

22.2

69.7

13

27

22.4

70.3

13 1/4

Z1

22.6

71.0

13 1/2

22.8

71.6

13 3/4

Z2

23.0

72.3

14

Z3

23.2

72.9

14 1/4

23.4

73.5

14 1/2

Z4

23.6

74.2

14 3/4

23.8

74.8

15

24.0

75.4

15 1/4

24.2

76.1

15 1/2

24.4

76.7

15 3/4

24.6

77.4

16