Ring Size Chart: US, UK, EU and Japan Conversion

Every ring size system measures the same thing, the inside of the ring, in a different way. The US and Canada use numbers, the UK, Ireland and Australia use letters, Europe uses the inside circumference in millimeters, and Japan uses its own numbers. This chart lines them all up. If you don’t know your size yet, the ring size finder measures a ring on your screen, or follow the guide to measuring ring size at home.

International ring size conversion chart

US / Canada	Inside diameter	Inside circumference	UK / Australia	EU / ISO	Japan
3	14.1 mm (0.55 in)	44.2 mm (1.74 in)	F	44	4
3½	14.5 mm (0.57 in)	45.5 mm (1.79 in)	G	45	5
4	14.9 mm (0.59 in)	46.8 mm (1.84 in)	H	47	7
4½	15.3 mm (0.60 in)	48.0 mm (1.89 in)	I	48	8
5	15.7 mm (0.62 in)	49.3 mm (1.94 in)	J½	49	9
5½	16.1 mm (0.63 in)	50.6 mm (1.99 in)	K½	51	10
6	16.5 mm (0.65 in)	51.9 mm (2.04 in)	L½	52	12
6½	16.9 mm (0.67 in)	53.1 mm (2.09 in)	M½	53	13
7	17.3 mm (0.68 in)	54.4 mm (2.14 in)	N½	54	14
7½	17.7 mm (0.70 in)	55.7 mm (2.19 in)	O½	56	15
8	18.1 mm (0.71 in)	57.0 mm (2.24 in)	P½	57	16
8½	18.5 mm (0.73 in)	58.2 mm (2.29 in)	Q¼	58	18
9	18.9 mm (0.75 in)	59.5 mm (2.34 in)	R½	60	19
9½	19.4 mm (0.76 in)	60.8 mm (2.39 in)	S½	61	20
10	19.8 mm (0.78 in)	62.1 mm (2.44 in)	T½	62	21
10½	20.2 mm (0.79 in)	63.3 mm (2.49 in)	U½	63	22
11	20.6 mm (0.81 in)	64.6 mm (2.54 in)	V½	65	24
11½	21.0 mm (0.83 in)	65.9 mm (2.59 in)	W½	66	25
12	21.4 mm (0.84 in)	67.2 mm (2.64 in)	X½	67	26
12½	21.8 mm (0.86 in)	68.5 mm (2.70 in)	Y½	68	27
13	22.2 mm (0.87 in)	69.7 mm (2.75 in)	Z½	70	29

Click a US size for its own page, with the ring drawn at actual size on your screen. Sizes between these exist in every system (US quarter sizes, UK half letters), and jewelers’ charts can differ by a quarter size, so for an expensive ring, go by the inside diameter in millimeters. Have a measurement already? The mm to ring size converter turns mm, cm or inches into a size.

How each system works

• US and Canada: each whole size adds 0.8128 mm (0.032 inch) to the inside diameter. The formula is: diameter in mm = 11.63 + 0.8128 × size. So size 7 = 11.63 + 5.69 = 17.3 mm.
• UK, Ireland, Australia, New Zealand: letters A to Z, with half sizes; sizes above Z are written Z+1, Z+2 and so on.
• Europe (ISO 8653): the inside circumference in millimeters. It’s the easiest system to measure yourself: wrap a paper strip around the finger and read the length in mm.
• Japan: sizes 1 to about 30; each step adds ⅓ mm to the diameter, starting at 13 mm for size 1. India and some Asian sellers use the same numbers, but check the seller’s chart.

Common ring sizes

	Most common range	Average
Women (US)	5½ to 7½	6
Men (US)	8 to 12	9

These are averages from jeweler surveys, not a substitute for measuring. Ring size also depends on the finger (the dominant hand is often a quarter to half size larger) and on the time of day: fingers are larger when warm and later in the day.

Tips for choosing the right size

• Between two sizes? Pick the larger one. A slightly loose ring can be fitted with a sizer bead; one that won’t pass the knuckle can’t be worn.
• Wide bands (6 mm and wider) fit tighter. Go up a quarter or half size.
• Large knuckles: measure the knuckle as well as the base of the finger, and choose a size between the two.
• Converting a ring you already own: measure its inside diameter edge to edge with a mm ruler, then find the closest diameter in the chart. For a paper-based option, use the printable ring sizer.