How to Measure Ring Size

To measure your ring size, wrap a strip of paper or string snugly round the base of the finger, mark where it overlaps, measure that length in millimetres and type it here: it is your finger’s circumference. 54 mm around, for example, is US 6¾, UK N, EU 54. If your knuckle is larger, type that too and the tool picks a size that passes it.

Your size

US 6¾

UK N · EU 54 · Japan 14

54 mm around the finger is a circumference of 54 mm and an inner diameter of 17.19 mm. That is almost exactly a US 6¾.

US / Canada 6¾ (exact)
UK / Australia N (exact)
EU / ISO 54 (exact)
Japan 14 (−0.5 mm)
Inner diameter 17.19 mm (0.677 in)
Inner circumference 54 mm (2.13 in)

US	Diameter mm	Circumference mm	UK	EU / ISO	Japan
3	14.07	44.2	F½	44	4
3½	14.47	45.5	G½	45.5	5
4	14.88	46.8	H½	47	7
4½	15.29	48	I½	48	8
5	15.69	49.3	J½	49.5	9
5½	16.1	50.6	K½	50.5	10
6	16.51	51.9	L½	52	12
6½	16.91	53.1	M½	53	13
7 ◀	17.32	54.4	N½	54.5	14
7½	17.73	55.7	O½	55.5	15
8	18.13	57	P½	57	16
8½	18.54	58.2	Q½	58	18
9	18.95	59.5	R½	59.5	19
9½	19.35	60.8	S½	61	20
10	19.76	62.1	T½	62	21
10½	20.16	63.3	U½	63.5	22
11	20.57	64.6	V½	64.5	24
11½	20.98	65.9	W½	66	25
12	21.38	67.2	X½	67	26
12½	21.79	68.5	Z	68.5	27
13	22.2	69.7	Z+1	69.5	29
13½	22.6	71	Z+2	71	30
14	23.01	72.3	Z+3	72.5	31
14½	23.42	73.6	Z+4	73.5	32
15	23.82	74.8	Z+5	75	33

How does a length become a ring size?

The strip’s length is the inner circumference. Diameter = length ÷ π. US size = (diameter − 11.63) ÷ 0.8128, to the nearest quarter. With a larger knuckle: use the circumference halfway between the base and the knuckle.

Worked example. A strip measures 54 mm: diameter 54 ÷ π = 17.19 mm; US (17.19 − 11.63) ÷ 0.8128 = 6.84, nearest US 6¾; UK (54 − 37.5) ÷ 1.25 = 13.2, nearest N; EU 54; Japan 14. If the knuckle measures 56 mm, the tool uses 55 mm, which is US 7¼ (a 56 mm knuckle alone would be US 7½).

Step by step

Cut a strip of paper about 5 mm wide and 10 cm long. Wrap it round the finger where the ring will sit, pull it snug, and mark with a pen where the end overlaps. Unwrap, lay it flat against a ruler, and read the distance from the end to the mark in millimetres. Repeat twice more; if the three readings differ by more than 2 mm, the wrap was too loose or too tight.

Measuring someone else without them knowing

Borrow a ring they wear on that finger and measure its inside with a ruler, or lay it on the on-screen sizer or the printable circles. Pressing the ring into a bar of soap and measuring the impression also works. Asking a friend of theirs is the usual last resort.

Inches and centimetres

Choose the unit you measured in; the tool converts at 25.4 mm to the inch. 2⅛ inches is 54 mm; 2¼ inches is 57 mm, about a size and a quarter larger, which shows why millimetres are the better unit for this job.

Questions about measuring at home

What do I need to measure my ring size at home?

A strip of paper about 5 mm wide, or a piece of string, a pen and a ruler with millimetres. Wrap the strip round the base of the finger, mark where it overlaps, lay it flat and measure from the end to the mark. That length is your circumference; type it in.

How tight should the strip be?

Snug, as a ring would sit: it should not dig in, and it should not slide freely. Paper is better than string because it does not stretch; thin ribbon is worse than both.

What about my knuckle?

Measure the knuckle too if it is larger than the base of the finger, and type both. The tool picks a size between the two, so the ring passes the knuckle without spinning once on. A ring that only fits the base may not go on at all.

When should I measure?

At the end of the day, at room temperature, when fingers are at their usual size; not first thing in the morning, after a cold walk or after a salty meal. Measure three times and use the middle value.

How accurate is this?

To about half a US size with care, which is enough for a plain band that can be resized and close enough to order a ring sizer set for anything expensive. A jeweller’s steel gauge is the final word.