Ring Size by Circumference: Finger mm to US, UK, EU

If you wrapped a string or paper strip around your finger, the length you measured is your finger circumference, and it maps directly to a ring size. 52 mm around is US 6, 54 mm is US 7, 57 mm is US 8 and 60 mm is US 9. The EU/ISO size is simply the circumference in mm. Find your measurement in the table below.

Ring size by finger circumference

Rows are every millimetre from 44 to 75 mm. The diameter column shows the matching ring diameter (circumference ÷ 3.1416).

Finger circumference (mm)	In inches	Diameter (mm)	Nearest US	Nearest UK	EU
44	1.73	14.0	3	F	44
45	1.77	14.3	3.5	G	45
46	1.81	14.6	3.5	G	46
47	1.85	15.0	4	H	47
48	1.89	15.3	4.5	I	48
49	1.93	15.6	5	J½	49
50	1.97	15.9	5.5	K½	50
51	2.01	16.2	5.5	K½	51
52	2.05	16.6	6	L½	52
53	2.09	16.9	6.5	M½	53
54	2.13	17.2	7	N½	54
55	2.17	17.5	7.5	O½	55
56	2.20	17.8	7.5	O½	56
57	2.24	18.1	8	P½	57
58	2.28	18.5	8.5	Q½	58
59	2.32	18.8	9	R½	59
60	2.36	19.1	9	R½	60
61	2.40	19.4	9.5	S½	61
62	2.44	19.7	10	T½	62
63	2.48	20.1	10.5	U½	63
64	2.52	20.4	10.5	U½	64
65	2.56	20.7	11	V½	65
66	2.60	21.0	11.5	W½	66
67	2.64	21.3	12	X½	67
68	2.68	21.6	12.5	Z	68
69	2.72	22.0	12.5	Z	69
70	2.76	22.3	13	Z+1	70
71	2.80	22.6	13.5	Z+2	71
72	2.83	22.9	14	Z+3	72
73	2.87	23.2	14.5	Z+4	73
74	2.91	23.6	14.5	Z+4	74
75	2.95	23.9	15	Z+5	75

How to measure your finger circumference

Cut a paper strip about 5 mm wide, or take a length of non-stretch thread or dental floss.
Wrap it once around the base of the finger the ring is for. It should be snug but able to slide over the knuckle.
Mark where the end overlaps with a fine pen. Do not let the strip twist.
Unroll it and measure from the end to the mark in millimetres.
Repeat twice more and use the middle value.

The printable ring sizer includes a pre-marked finger strip if you would rather not use a ruler.

Circumference in inches

Many tape measures in the US read in inches. Multiply by 25.4 to get millimetres: 2.1 in × 25.4 = 53.3 mm, which is between US 6.5 and 7. Common values:

1.9 in (48.3 mm) – US 4.5
2.0 in (50.8 mm) – US 5.5
2.1 in (53.3 mm) – US 6.5
2.2 in (55.9 mm) – US 7.5
2.3 in (58.4 mm) – US 8.5
2.4 in (61.0 mm) – US 9.5
2.5 in (63.5 mm) – US 10.5

Why finger measurements often come out too large or small

A string measurement is only as good as the tension you used. Pull 1 mm too tight and you lose almost half a size; leave it loose and you gain one. Thick string adds its own width: a 1 mm thread wrapped around a finger reads about 3 mm longer than the true circumference. That is why paper strips and thin floss give better results, and why measuring a ring you already own is more reliable still. If you have such a ring, use ring size by diameter or the on-screen ring sizer instead.

Knuckles and between sizes

A ring has to pass over the knuckle, so the knuckle sets the minimum size. If your knuckle measures 58 mm but the base of the finger is only 55 mm, a US 8.5 (58.1 mm) will pass the knuckle but may spin; a size in between, around US 8, is usually the best compromise. For wide bands of 6 mm or more, add about 1 mm of circumference (roughly half a size) to the reading.

From circumference to the other systems

EU / ISO: the circumference itself, rounded. 54 mm = EU 54.
Swiss: circumference minus 40. 54 mm = Swiss 14.
US: divide by 3.1416 for the diameter, then (diameter − 11.63) ÷ 0.8128.
UK, India and others: use the ring size converter.

Not sure of your ring size? Measure it on your phone screen in 30 seconds.

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Frequently asked questions

What ring size is 50 mm circumference?

50 mm around is a diameter of 15.9 mm, closest to US 5 (49.3 mm) or 5.5 (50.6 mm). Most people take US 5.5 / UK K½ / EU 50–51.

What ring size is 60 mm circumference?

60 mm is a diameter of 19.1 mm, which is US 9 (UK R½, EU 60).

What ring size is 2.5 inches around?

2.5 inches is 63.5 mm, which is US 10.5, UK U½ and EU 63.

Is EU ring size the same as circumference?

Yes. EU and ISO ring sizes are the inner circumference in millimetres, so a 54 mm finger is EU 54.