All sizes are approximate equivalents
British Standard	Inside Diameter	Inside Circumference	Equivalents
Ring Sizes	mm/inches	mm/inches	USA & Canadian	French	German	Japanese
C	12.78 / .503	40.2 / 1.580	1½	40½	12¾	—
D	13.21 / .520	41.5 / 1.634	2	41½	13¼	2
E	13.61 / .536	42.7 / 1.684	2½	42¾	13¾	3
F	14.04 / .553	44.0 / 1.739	3	44	14	4
G	14.45 / .569	45.2 / 1.788	3½	45¼	14½	—
H½	14.86 / .585	46.5 / 1.836	4	46½	15	7
I½	15.27 / .601	47.8 / 1.888	4½	47¾	15¼	8
J½	15.70 / .618	49.0 / 1.941	5	49	15¾	9
L	16.10 / .634	50.2 / 1.992	5½	50¼	16	—
M	16.51 / .650	51.5 / 2.042	6	51½	16½	12
M½	N/A	N/A	6¼	N/A	N/A	N/A
N	16.92 / .666	52.8 / 2.092	6½	52¾	17	13
N½	17.35 / .683	54.0 / 2.146	7	54	17¼	14
O½	17.63 / .699	55.3 / 2.196	7½	55½	17½	15
P½	18.19 / .716	56.6 / 2.249	8	56¾	18	16
Q½	18.59 / .732	57.8 / 2.300	8½	58	18½	17
R½	18.99 / .748	59.1 / 2.350	9	59¼	19	18
S½	19.41 / .764	60.3 / 2.400	9½	60½	19½	19
T½	19.84 / .781	61.6 / 2.463	10	61¾	20	20
U½	20.24 / .797	62.8 / 2.504	10½	62¾	20¼	22
V½	20.68 / .814	64.1 / 2.567	11	64¼	20¾	23
W½	21.01 / .830	66.0 / 2.608	11½	66	21	24
Y	21.41 / .846	67.3 / 2.658	12	67¼	21½	25