WITHIN · SIZES · Updated 10 October 2026

Ring size chart and converter

Ring sizes in US and Canada, UK and Australia, Europe, Japan and Singapore and inside diameter, side by side. Every number comes from a chart we name and date.

Sizes in the tables: 43 rows in 1 table
Systems: US and Canada, UK and Australia, Europe, Japan and Singapore and Inside diameter (mm)
Sources: 3 charts, each named under its table
Read: 9 October 2026

Ring sizes in every system, unisex

Ring sizes in every system. From Blue Nile, read 9 October 2026.
US and Canada	UK and Australia	Europe	Japan and Singapore	Inside diameter (mm)
3	F 1/2	44	4	14.1
	G	45	5	14.3
3.5	G 1/2			14.5
	H	46	6	14.7
4	H 1/2	47	7	14.9
	I			15.1
4.5	I 1/2	48	8	15.3
	J			15.5
5	J 1/2	49	9	15.7
	K	50		15.9
5.5	K 1/2		10	16.1
	L	51		16.3
6	L 1/2	52	11	16.5
	M		12	16.7
6.5	M 1/2	53	13	16.9
	N			17.1
7	N 1/2	54	14	17.3
	O	55		17.5
7.5	O 1/2		15	17.7
	P	56		17.9
8	P 1/2	57	16	18.1
	Q			18.3
8.5	Q 1/2	58	17	18.5
	R	59		18.8
9	R 1/2		18	19
	S	60		19.2
9.5	S 1/2	61	19	19.4
	T			19.6
10	T 1/2	62	20	19.8
	U		21	20
10.5	U 1/2	63	22	20.2
	V	64		20.4
11	V 1/2		23	20.6
	W	65		20.8
11.5	W 1/2	66	24	21
	X			21.2
12	X 1/2	67	25	21.4
	Y			21.6
12.5	Z	68	26	21.8
	Z 1/2	69		22
13		70	27	22.2
	Z+1			22.4
13.5	Z+2			22.6

Blue Nile's chart goes up in steps of about 0.2 mm, so not every system has a size on every row. A blank cell means that system has no size at that width.
On Cartier's chart the European size and the finger size in millimetres are the same number.
Japanese sizes differ a little from one jeweller to the next. Cartier's chart puts a US 6 at Japan 12, where Blue Nile puts it at Japan 11. This table follows Blue Nile.
Blue Nile's chart prints the UK size N one column to the left, under Europe. We show it under UK.

Source: Blue Nile (bn-dam.services.r2net.com), read 9 October 2026.

How to measure at home

Take a ring that fits the finger you want to size.
Print Blue Nile's ring sizer at 100% scale. A credit card, 54 mm tall, should fit inside the outline on the sheet.
Lay the ring on the circles. The right circle just fills the inside of the ring. Its number is the inside diameter in mm, so look for it in the last column.
If you have no ring, wrap a strip of paper or string around the base of the finger and mark where the ends meet. Lay it flat and measure it in mm. That length is close to your European size.
Measure in the evening. Fingers change size a little through the day.
If you fall between two sizes, take the larger one. A wide band can feel tight, so you may need a half size up.

Sources: Blue Nile (bn-dam.services.r2net.com), read 9 October 2026, Tiffany & Co. (tiffany.com), read 9 October 2026 and Cartier (cartier.com), read 9 October 2026.

Common questions

What is a US size 7 ring in UK sizes?

A UK N 1/2. On the same row of Blue Nile's chart, a US 7 is a European 54 and a Japanese 14, with an inside diameter of 17.3 mm.

What is a UK ring size P 1/2 in US sizes?

A US 8. Blue Nile's chart puts UK P 1/2 at European 57 and Japanese 16, with an inside diameter of 18.1 mm.

What US ring size is a European 54?

A US 7. On Blue Nile's chart the same ring is a UK N 1/2 and a Japanese 14.

Are Japanese ring sizes the same as US sizes?

No. A US 7 is a Japanese 14 on Blue Nile's chart. Japanese sizes also vary a little between jewellers: Cartier puts a US 6 at Japan 12, Blue Nile at Japan 11.

What if I am between two ring sizes?

Take the larger size. Blue Nile, Tiffany and Cartier all say so. A wide band can feel tighter, so Blue Nile says you may need to go up a half size.

Shop rings in your size

Every piece on within shows the size its boutique printed and how many are left in it.

Designer size charts

Tom Wood size chart

Other size charts

Sources

Blue Nile: Ring sizes for the US and Canada, the UK and Australia, Europe and Japan by inside diameter, and how to size a ring you already own. bn-dam.services.r2net.com, read 9 October 2026.
Tiffany & Co.: US ring sizes with inside diameter and circumference in mm, and how to measure a finger with string. tiffany.com, read 9 October 2026.
Cartier: Cartier's ring chart by finger size in mm, with European, US, UK and Japanese sizes. cartier.com, read 9 October 2026.