A Comprehensive Ring Size Chart / Ring Size Conversion Chart

A Comprehensive Ring Size Chart for US ring size, British/Irish/Australia ring size, Swiss, EURO and Japanese size plus mm and inches conversion.
In Austria, France, Germany, Belgium and Scandinavia, ring sizes are specified using actual internal circumference in mm (the same as the ISO standard).

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US/Canada Ring sizes	Inner Diameter	Inner Diameter	Inner Circum- ference	Inner Circum- ference	British, Irish, Australian sizes	Japanese sizes	Swiss/Italy/ Spain/ Netherlandssizes
Standard	(inches)	(mm)	(inches)	(mm)	Equivalent	Equivalent	Equivalent
0	0.458	11.6	1.438	36.5
1/4	0.466	11.8	1.463	37.2
1/2	0.474	12.0	1.488	37.8	A
3/4	0.482	12.2	1.513	38.4	A 1/2
1	0.490	12.4	1.539	39.1	B	1
1 1/4	0.498	12.6	1.564	39.7	B 1/2
1 1/2	0.506	12.9	1.589	40.4	C
1 3/4	0.514	13.1	1.614	41.0	C 1/2
2	0.522	13.3	1.639	41.6	D	2	1.50
2 1/4	0.530	13.5	1.664	42.3	D 1/2
2 1/2	0.538	13.7	1.689	42.9	E	3	2.75
2 3/4	0.546	13.9	1.714	43.5	E 1/2
3	0.554	14.1	1.740	44.2	F	4	4.00
3 1/4	0.562	14.3	1.765	44.8	F 1/2	5	5.25
3 1/2	0.570	14.5	1.790	45.5	G
3 3/4	0.578	14.7	1.815	46.1	G 1/2	6	6.50
4	0.586	14.9	1.840	46.7	H	7
4 1/4	0.594	15.1	1.865	47.4	H 1/2		7.75
4 1/2	0.602	15.3	1.890	48.0	I	8
4 3/4	0.610	15.5	1.915	48.7	J		9.00
5	0.618	15.7	1.941	49.3	J 1/2	9
5 1/4	0.626	15.9	1.966	49.9	K		10.00
5 1/2	0.634	16.1	1.991	50.6	K 1/2	10
5 3/4	0.642	16.3	2.016	51.2	L		11.75
6	0.650	16.5	2.041	51.8	L 1/2	11	12.75
6 1/4	0.658	16.7	2.066	52.5	M	12
6 1/2	0.666	16.9	2.091	53.1	M 1/2	13	14.00
6 3/4	0.674	17.1	2.116	53.8	N
7	0.682	17.3	2.141	54.4	N 1/2	14	15.25
7 1/4	0.690	17.5	2.167	55.0	O
7 1/2	0.698	17.7	2.192	55.7	O 1/2	15	16.50
7 3/4	0.706	17.9	2.217	56.3	P
8	0.714	18.1	2.242	56.9	P 1/2	16	17.75
8 1/4	0.722	18.3	2.267	57.6	Q
8 1/2	0.730	18.5	2.292	58.2	Q 1/2	17
8 3/4	0.738	18.7	2.317	58.9	R		19
9	0.746	18.9	2.342	59.5	R 1/2	18
9 1/4	0.754	19.2	2.368	60.1	S		20.25
9 1/2	0.762	19.4	2.393	60.8	S 1/2	19
9 3/4	0.770	19.6	2.418	61.4	T		21.5
10	0.778	19.8	2.443	62.1	T 1/2	20
10 1/4	0.786	20.0	2.468	62.7	U	21
10 1/2	0.794	20.2	2.493	63.3	U 1/2	22	22.75
10 3/4	0.802	20.4	2.518	64.0	V
11	0.810	20.6	2.543	64.6	V 1/2	23
11 1/4	0.818	20.8	2.569	65.2	W		25
11 1/2	0.826	21.0	2.594	65.9	W 1/2	24
11 3/4	0.834	21.2	2.619	66.5	X
12	0.842	21.4	2.644	67.2	X 1/2	25	27.50
12 1/4	0.850	21.6	2.669	67.8	Y
12 1/2	0.858	21.8	2.694	68.4	Z	26	28.75
12 3/4	0.866	22.0	2.719	69.1	Z 1/2
13	0.874	22.2	2.744	69.7		27
13 1/4	0.882	22.4	2.769	70.3	Z1
13 1/2	0.890	22.6	2.795	71.0
13 3/4	0.898	22.8	2.820	71.6	Z2
14	0.906	23.0	2.845	72.3	Z3
14 1/4	0.914	23.2	2.870	72.9
14 1/2	0.922	23.4	2.895	73.5	Z4
14 3/4	0.930	23.6	2.920	74.2
15	0.938	23.8	2.945	74.8	Z5
15 1/4	0.946	24.0	2.970	75.4
15 1/2	0.954	24.2	2.996	76.1
15 3/4	0.962	24.4	3.021	76.7	Z6
16	0.970	24.6	3.046	77.4

Further notes and info:
There are several systems for denoting the sizes of jewellery rings in use around the world:

The ISO standard for ring sizes is ISO 8653:1986, which defines standard ring sizes in terms of the inner circumference of the ring measured in millimetres.

In the United States and Canada, ring sizes are specified using a numerical scale, with quarter and half sizes. An increase of a full size is an increase of 0.032 inch (0.8128 mm) in diameter, or roughly 1/10 inch (more precisely, 0.1005 in or 2.55 mm) in inside circumference.

In Ireland, the United Kingdom and Australia, ring sizes are specified using an alphabetical scale, with half sizes.

In India, Japan and China, ring sizes are specified using a numerical scale, that only has whole sizes, and does not have simple linear correlation with diameter or circumference.

In Austria, France, Germany, Belgium and Scandinavia, ring sizes are specified using actual internal circumference in mm (the same as the ISO standard). In some countries, half sizes may be used.

In Italy, Spain, Netherlands, and Switzerland, ring sizes are specified as the circumference minus 40mm. A 50 in Germany will be a 10 in Switzerland.(Source: wikipedia.org)