Ring size

A Bergeon ring sizing stick. (ISO 8653:1986 and number scales)

Ring size is a measurement used to denote the circumference of jewellery rings.

Systems

There are several systems for denoting the sizes of jewellery rings in use around the world:^[1]

• 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,^[2] 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.

Equations

• US, Canada, Mexico: ring_inside_circumference = 36.5 mm + 2.55 mm × ring_size
• US, Canada, Mexico: ring_diameter = 11.63 mm + 0.8128 mm × ring_size

Conversion chart for ring sizes

Inside diameter		Inside circumference		Sizes
(in)	(mm)	(in)	(mm)	United States, Canada and Mexico	United Kingdom, Ireland, Australia and New Zealand	China, Japan, South America	India	Italy, Spain, Netherlands, Switzerland
0.458	11.63	1.44	36.5	0
0.466	11.84	1.46	37.2	¼
0.474	12.04	1.49	37.8	½	A
0.482	12.24	1.51	38.5	¾	A½
0.49	12.45	1.54	39.1	1	B	1
0.498	12.65	1.56	39.7	1¼	B½
0.506	12.85	1.59	40.4	1½	C			0.5
0.514	13.06	1.61	41	1¾	C½		1	1
0.522	13.26	1.64	41.7	2	D	2	2	1.75
0.53	13.46	1.67	42.3	2¼	D½			2.25
0.538	13.67	1.69	42.9	2½	E	3	3	3
0.546	13.87	1.72	43.6	2¾	E½		4	3.5
0.554	14.07	1.74	44.2	3	F	4		4.25
0.562	14.27	1.77	44.8	3¼	F½	5	5	4.75
0.57	14.48	1.79	45.5	3½	G			5.5
0.578	14.68	1.82	46.1	3¾	G½	6	6	6
0.586	14.88	1.84	46.8	4	H	7		6.75
0.594	15.09	1.87	47.4	4¼	H½		7	7.5
0.602	15.29	1.89	48	4½	I	8	8	8
0.61	15.49	1.92	48.7	4¾	J		9	8.75
0.618	15.7	1.94	49.3	5	J½	9		9.25
0.626	15.9	1.97	50	5¼	K		10	10
0.634	16.1	1.99	50.6	5½	K½	10		10.5
0.642	16.31	2.02	51.2	5¾	L		11	11.25
0.65	16.51	2.04	51.9	6	L½	11	12	11.75
0.658	16.71	2.07	52.5	6¼	M	12		12.5
0.666	16.92	2.09	53.1	6½	M½	13	13	13.25
0.674	17.12	2.12	53.8	6¾	N			13.75
0.682	17.32	2.14	54.4	7	N½	14	14	14.5
0.69	17.53	2.17	55.1	7¼	O		15	15
0.698	17.73	2.19	55.7	7½	O½	15		15.75
0.706	17.93	2.22	56.3	7¾	P		16	16.25
0.714	18.14	2.24	57	8	P½	16	17	17
0.722	18.34	2.27	57.6	8¼	Q			17.5
0.73	18.54	2.29	58.3	8½	Q½	17	18	18.25
0.738	18.75	2.32	58.9	8¾	R		19	19
0.746	18.95	2.34	59.5	9	R½	18		19.5
0.754	19.15	2.37	60.2	9¼	S		20	20.25
0.762	19.35	2.39	60.8	9½	S½	19	21	20.75
0.77	19.56	2.42	61.4	9¾	T			21.5
0.778	19.76	2.44	62.1	10	T½	20	22	22
0.786	19.96	2.47	62.7	10¼	U	21	23	22.75
0.794	20.17	2.49	63.4	10½	U½	22		23.25
0.802	20.37	2.52	64	10¾	V		24	24
0.81	20.57	2.54	64.6	11	V½	23	25	24.75
0.818	20.78	2.57	65.3	11¼	W			25.25
0.826	20.98	2.59	65.9	11½	W½	24	26	26
0.834	21.18	2.62	66.6	11¾	X			26.5
0.842	21.39	2.65	67.2	12	X½	25	27	27.25
0.85	21.59	2.67	67.8	12¼	Y		28	27.75
0.858	21.79	2.7	68.5	12½	Z	26		28.5
0.866	22	2.72	69.1	12¾	Z½		29	29
0.874	22.2	2.75	69.7	13		27	30	29.75
0.882	22.4	2.77	70.4	13¼	Z1			30.5
0.89	22.61	2.8	71	13½			31	31
0.898	22.81	2.82	71.7	13¾	Z2		32	31.75
0.906	23.01	2.85	72.3	14	Z3			32.25
0.914	23.22	2.87	72.9	14¼			33	33
0.922	23.42	2.9	73.6	14½	Z4			33.5
0.93	23.62	2.92	74.2	14¾			34	34.25
0.938	23.83	2.95	74.8	15			35	34.75
0.946	24.03	2.97	75.5	15¼				35.5
0.954	24.23	3	76.1	15½			36	36.25
0.962	24.43	3.02	76.8	15¾				36.75
0.97	24.64	3.05	77.4	16			37	37.5

Ring sizes can be measured physically by a plastic or metal ring sizer, or by measuring the girth of a ring that already fits. There are also online measuring tools available.

References

1. "Ring Finger Sizes".
2. PDF Ring sizer with Australian Sizes