International ring size chart

Common ring sizes from US 3 to 13 across five systems, plus diameter and circumference in millimetres. Values derive from the US diameter scale and are cross-checked against published ISO/JIS charts.

Diameter and circumference are different measurements Diameter crosses the empty inside of a ring. Circumference follows the complete inner edge. Inner diameterInner circumference

Swipe or scroll sideways to compare every column.

International ring size chart
US / CA	UK / AU	EU / ISO	Japan	CH / IT / ES	Inner diameter, millimetres	Circ mm	Ø in
3	F½	44	4	4	14.07	44.2	0.554
3.5	G½	45	5	5	14.48	45.5	0.570
4	H½	47	7	7	14.88	46.8	0.586
4.5	I½	48	8	8	15.29	48.0	0.602
5	J½	49	9	9	15.70	49.3	0.618
5.5	K½	51	10	11	16.10	50.6	0.634
6	L½	52	12	12	16.51	51.9	0.650
6.5	M½	53	13	13	16.92	53.1	0.666
7	N½	54	14	14	17.32	54.4	0.682
7.5	O½	56	15	16	17.73	55.7	0.698
8	P½	57	16	17	18.14	57.0	0.714
8.5	Q½	58	17	18	18.54	58.3	0.730
9	R½	60	18	20	18.95	59.5	0.746
9.5	S½	61	19	21	19.35	60.8	0.762
10	T½	62	20	22	19.76	62.1	0.778
10.5	U½	63	22	23	20.17	63.4	0.794
11	V½	65	23	25	20.57	64.6	0.810
11.5	W½	66	24	26	20.98	65.9	0.826
12	Y	67	25	27	21.39	67.2	0.842
12.5	Z	68	26	28	21.79	68.5	0.858
13	Z½	70	27	30	22.20	69.7	0.874

How to read this chart

Find the size you know in its column, then read across for the equivalents. If you measured a finger or an existing ring in millimetres, match the Ø mm (inner diameter) or Circ mm (inner circumference) column. If your measurement falls between rows, use the interactive converter.

Notes on accuracy

EU/ISO numbers are the inner circumference in mm (ISO 8653).
UK uses half letters (US 7 = UK N½); whole-letter charts are often off by a size.
Japan, India and China are lookup-based and can differ by up to a full size between charts.
Switzerland / Italy / Spain ≈ circumference in mm minus 40.

Frequently asked questions

What size is a 17 mm ring?

A 17.3 mm inner diameter is a US 7 (UK N½, EU 54). 17 mm is just under US 7 — closest to US 6.75–7.

Does EU ring size equal the circumference?

Yes. Under ISO 8653 the EU/ISO size number is the inner circumference in millimetres, so EU 54 means a 54 mm circumference.

Why do UK sizes use half letters like N½?

US whole sizes fall between UK whole letters, so the accurate UK equivalent is usually a half letter. Charts that show only whole letters are often wrong by up to a full size.