Free Tool

Ring Size Calculator

Find your ring size from a quick finger measurement, or convert a known size between US, UK, EU and Japanese systems — all in one place.

Measure your finger

Wrap a strip of paper or string around your finger, mark where it overlaps, and measure the length in millimetres — that's your circumference. Or measure the inside diameter of a ring that fits.

What did you measure?

Finger circumference

Your ring size

US 7

Closest standard size to your measurement.

US / Canada

UK / Australia

EU / ISO

Japan / China

Diameter

17.3 mm

Circumference

54.4 mm

Measure at the end of the day when fingers are warm, and size for the widest knuckle the ring must pass over. Wide bands fit tighter — go up a half size for bands over 6 mm.

Ring size conversion chart

The full international ring size chart, matched to the band's inside diameter and circumference in millimetres.

US / Canada	UK / Australia	EU / ISO	Japan / China	Diameter	Circumference
3	F	44	4	14.0 mm	44.0 mm
3.5	G	45	5	14.4 mm	45.5 mm
4	H	47	7	14.8 mm	46.8 mm
4.5	I	48	8	15.2 mm	48.0 mm
5	J½	49	9	15.7 mm	49.3 mm
5.5	L	51	10	16.1 mm	50.6 mm
6	M	52	11	16.5 mm	51.9 mm
6.5	N	53	13	16.9 mm	53.1 mm
7	O	54	14	17.3 mm	54.4 mm
7.5	P	56	15	17.7 mm	55.7 mm
8	Q	57	16	18.2 mm	57.0 mm
8.5	Q½	58	17	18.6 mm	58.3 mm
9	R½	60	18	19.0 mm	59.5 mm
9.5	S½	61	19	19.4 mm	60.8 mm
10	T½	62	20	19.8 mm	62.1 mm
10.5	U½	64	22	20.2 mm	63.4 mm
11	V½	65	23	20.6 mm	64.6 mm
11.5	W½	66	24	21.0 mm	65.9 mm
12	X½	68	25	21.4 mm	67.2 mm
12.5	Z	69	26	21.8 mm	68.5 mm
13	Z½	70	27	22.2 mm	69.7 mm

Shopping for a birthstone ring? Browse our birthstone jewellery guide or value a stone with the diamond price calculator.

Frequently Asked Questions

How do I measure my ring size at home?

Wrap a strip of paper or a piece of string around the base of your finger, mark where it overlaps, then measure that length in millimetres — that is your finger circumference. Enter it in the calculator above to get your ring size. Alternatively, measure the inside diameter of a ring that already fits.

What is the average ring size?

For women, the most common ring sizes are US 5 to 7 (UK J½ to O), with US 6 being a frequent average. For men, US 9 to 11 (UK R½ to V½) is typical, with US 10 a common average. Hand size, not height, is the best guide.

How do US, UK and EU ring sizes compare?

US and Canadian sizes are numeric (e.g. 7). UK, Irish and Australian sizes use letters (US 7 ≈ UK O). EU/ISO sizes equal the inside circumference in millimetres (US 7 ≈ EU 54). Japanese and Chinese sizes use their own numeric scale (US 7 ≈ JP 14). Use the converter above to switch between them.

Should I size up for a wide band?

Yes. A wider band covers more of your finger and fits more snugly, so for bands wider than about 6 mm it is common to go up a half size for comfort. It is also best to measure at the end of the day when your fingers are at their warmest and largest.

How accurate is an online ring size calculator?

It is accurate to the nearest standard size when your measurement is precise, which is ideal for choosing a starting size or a surprise gift. For an expensive ring, confirm with a jeweller’s sizing gauge before buying, as finger shape and knuckle size also affect the fit.