Circumference (mm) Diameter (mm) Europe UK & Australia United States & Canada China Singapore & Japan Hong Kong Switzerland 44.2 14.1 44 F½ 3 6 4 6 4 44.8 14.3 45 G 5 5¼ 45.5 14.5 G½ 3½ 7 7.5 46.1 14.7 46 H 6 6½ 46.8 14.9 47 H½ 4 8 7 9 47.4 15.1 I 9 7¾ 48.0 15.3 48 I½ 4½ 8 10 48.7 15.5 J 9 49.3 15.7 49 J½ 5 10 9 11 50.0 15.9 50 K 10 50.6 16.1 K½ 5½ 11 10 12 51.2 16.3 51 L 11¾ 51.9 16.5 52 L½ 6 12 11 13 12¾ 52.5 16.7 M 13 12 53.1 16.9 53 M½ 6½ 13 14.5 14 53.8 17.1 N 14 54.4 17.3 54 N½ 7 14 16 15¼ 55.1 17.5 55 O 15 55.7 17.7 O½ 7½ 15 17 16½ 56.3 17.9 56 P 16 57.0 18.1 57 8 17 16 17¾ 57.2 18.2 P½ 18 57.6 18.3 Q 58.3 18.5 58 Q½ 8½ 18 17 19 58.9 18.8 59 R 19 59.5 19.0 R½ 9 19 18 20.5 60.2 19.2 60 S 20 20¼ 60.8 19.4 61 S½ 9½ 19 22 61.4 19.6 T 21 21½ 62.1 19.8 62 T½ 10 20 23 62.7 20.0 U 22 21 63.4 20.2 63 U½ 10½ 22 24 22¾ 64.0 20.4 64 V 23 64.6 20.6 V½ 11 23 25 65.3 20.8 65 W 24 25 65.9 21.0 66 W½ 11½ 25 24 26 66.6 21.2 X 67.2 21.4 67 X½ 12 26 25 27.75 27½ 67.8 21.6 Y 68.5 21.8 68 Z 12½ 26 28¾ 69.1 22.0 69 Z½ 69.7 22.2 70 13 27 30 70.4 22.4 Z+1 71.0 22.6 Z+2 13½