Ring Size Converter

Convert ring sizes between US, UK/Australia letters, EU (ISO 8653), Swiss and Japanese sizes, or find your size from a ring's inner diameter or circumference in mm.

Size

System

UK, Ireland, Australia, NZ

N½

EU / ISO (circumference mm)

54.5

Switzerland

14.5

Japan & China

Inner diameter (mm)

17.32

Inner circumference (mm)

54.41

Ring size chart

US ring sizes with UK, EU, Swiss and Japanese sizes, inner diameter and circumference
US	UK / AU	EU	Swiss	Japan	Diameter (mm)	Circumference (mm)
4	H½	47	7	7	14.88	46.75
4.5	I½	48	8	8	15.29	48.03
5	J½	49.5	9.5	9	15.69	49.30
5.5	K½	50.5	10.5	10	16.10	50.58
6	L½	52	12	12	16.51	51.86
6.5	M½	53	13	13	16.91	53.13
7	N½	54.5	14.5	14	17.32	54.41
7.5	O½	55.5	15.5	15	17.73	55.69
8	P½	57	17	16	18.13	56.96
8.5	Q½	58	18	18	18.54	58.24
9	R½	59.5	19.5	19	18.95	59.52
9.5	S½	61	21	20	19.35	60.79
10	T½	62	22	21	19.76	62.07
10.5	U½	63.5	23.5	22	20.16	63.35
11	V½	64.5	24.5	24	20.57	64.63
11.5	W½	66	26	25	20.98	65.90
12	X½	67	27	26	21.38	67.18
13	Z+1	69.5	29.5	29	22.20	69.73

Wide bands (over 6 mm) fit tighter: go up a quarter to half US size. Jewellers' mandrels can differ by a quarter size, so confirm with the seller's own chart before ordering an engraved or unresizable ring.

How to use it

Choose the system your size is in, type it (UK sizes are letters, such as L or L½) and every other system appears at once, rounded the way jewellers sell them: US in quarter sizes, UK in half letters, EU and Swiss in half sizes and Japan in whole numbers. A US 7 is a UK N½, an EU 54.5, a Swiss 14.5 and a Japanese 14, with a 17.32 mm inner diameter.

No ring to hand? Wrap a strip of paper around the base of your finger, mark where it overlaps, and measure the length in millimetres. Choose inner circumference and type that number. To size from a ring that already fits, measure straight across the inside and choose inner diameter.

How each system is defined

The international standard ISO 8653 numbers a ring by its inner circumference in millimetres, which is the EU size: an EU 52 has a 52 mm inside circumference. Switzerland uses the same measure minus 40, so a Swiss 12 is also 52 mm.

US and Canadian sizes go up in steps of 0.032 inch (0.8128 mm) of inner diameter, starting from 11.63 mm at size 0, so a US 6 is 16.51 mm across. UK, Irish, Australian and New Zealand sizes (British Standard 6820) are letters: A is 37.5 mm around and each letter adds 1.25 mm. Japanese and Chinese sizes (JCS) start at No. 1 = 13.0 mm diameter and add a third of a millimetre per number.

Getting the fit right

Measure at the end of the day, when fingers are largest, and not when your hands are cold. A ring has to pass over the knuckle, so if your knuckle is much wider than the base of your finger, size between the two. Bands wider than about 6 mm fit tighter, so go up a quarter to a half US size.

Gear for this job

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Frequently asked questions

What is a US 7 ring in UK and EU sizes?

UK N½ and EU 54.5 (54.4 mm inner circumference), Swiss 14.5 and Japanese 14. The inner diameter is 17.32 mm.

How do I convert UK ring letters to US sizes?

Each UK letter is 1.25 mm of circumference and each US size is about 2.55 mm, so two UK letters make roughly one US size. L½ is a US 6, N½ a US 7 and P½ a US 8.

What ring size is 17 mm?

A 17 mm inner diameter is about a US 6.5 to 6.75, UK M½ to N, and EU 53.5. Type 17 with inner diameter selected for the exact figure.

Are EU ring sizes the circumference in mm?

Yes. Under ISO 8653 the size number is the inner circumference in millimetres, so EU 54 is a ring 54 mm around the inside.

Are Japanese and Chinese ring sizes the same?

They follow the same JCS numbering in most shops, where No. 1 is 13 mm across and each number adds about 0.33 mm. A US 6 is about a Japanese 12.