Ring Size Converter

Convert US, UK, European, Japan, Switzerland, and mm ring sizes — instantly.

Free ring size converter. Convert US, UK, European (ISO mm), Japan/Asia, Switzerland, inner circumference, and inner diameter using published equivalency charts. Approximate guidance — measure for important purchases. Use the converter above for any system pair — full charts are below.

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7 US & Canada = N½ UK & Australia

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Complete ring size conversion chart

Full equivalency table — US & Canada, UK & Australia, European (ISO circumference mm), Japan / Asia, Switzerland, inner circumference (mm), and inner diameter (mm) for every published row. Source: Wikipedia "Ring size" equivalency table (ISO 8653:2016, BSI, Bureau of Standards Circular No. 43).

US & Canada	UK & Australia	EU (ISO mm)	Japan / Asia	Switzerland	Inner circumference (mm)	Inner diameter (mm)
3	F	44	4	4.2	44.2	14.07
3.5	G	45	—	5.5	45.5	14.48
4	H	46	7	6.8	46.8	14.88
4.5	I	48	8	8	48	15.29
5	J½	49	9	9.3	49.3	15.7
5.25	K	50	10	10	50	15.9
5.5	K½	50	—	10.6	50.6	16.1
6	L½	51	11	11.9	51.9	16.51
6.25	M	52	12	12.5	52.5	16.71
6.5	M½	52	13	13.1	53.1	16.92
7	N½	54	14	14.4	54.4	17.32
7.5	O½	55	15	15.7	55.7	17.73
8	P½	57	16	17	57	18.14
8.5	Q¼	58	17	18.3	58.3	18.54
9	R½	59	18	19.5	59.5	18.95
9.5	S½	60	19	20.8	60.8	19.35
10	T½	61	20	22.1	61.9	19.76
10.5	U½	63	22	23.4	63.2	20.17
11	V½	64	23	24.6	64.5	20.57
11.5	W½	65	24	25.9	65.8	20.98
12	X½	67	25	27.2	67.1	21.36
12.5	Y½	68	26	28.5	68.4	21.77
13	Z½	69	27	29.7	69.7	22

How to convert ring sizes

Select your sizing system and ring size above. We look up the matching row by inner circumference (the canonical basis), then read the equivalent in your target system. Inner circumference (mm) and inner diameter (mm) convert directly — diameter uses exact π. When a named column has no value on the exact row, the nearest row with a published target size is used and labeled (nearest).

Measure inner circumference with a strip of paper around the finger (or use a ring that fits). For important purchases, confirm with a jeweller — finger size changes with temperature and time of day.

Ring size systems explained

US & Canada: Numbered scale with quarter and half sizes (e.g. 7, 7.5).
UK & Australia: Letter-based scale (e.g. M, N½) with half-letter steps.
European (ISO mm): ISO 8653 inner circumference in millimeters (whole numbers on this chart).
Japan / Asia: East Asian numbered scale; not every US/UK row has a published JP equivalent in the source table.
Switzerland: Swiss numbered scale with decimal steps.
Inner circumference / diameter (mm): Physical measurements — circumference is the chart basis; diameter = circumference ÷ π.

Frequently asked questions

How do I convert ring sizes between US, UK, and EU?

Select your current system and ring size above, then pick the target system. We look up the matching inner-circumference row in our cited chart and read the equivalent. Example: US & Canada 7 = UK & Australia N½. Inner circumference (mm) is the canonical basis — measure with a paper strip or use a ring that fits well.

Are ring size conversions exact?

Conversions use published equivalency rows — not a linear formula. When a target column is blank on the exact row, the nearest row with a published value is used and labeled "(nearest)". This is guidance based on published charts — not a guarantee of fit. Confirm with a jeweller for important purchases.

Is this ring size converter private?

Yes. All lookups run locally in your browser. Nothing you select is sent to a server.