How do I measure my ring size at home?

Wrap a strip of paper around the base of your finger, mark where it overlaps, and measure the length in mm — this is your inner circumference. Find that value in the EU column of the table to get your ring size. Measure in the afternoon when fingers are slightly larger.

What does the EU ring size number represent?

EU ring sizes (also the ISO 8653 standard) represent the inner circumference of the ring in millimeters. EU size 52 means the ring's inner circumference is 52 mm. This is the most direct measurement-based system.

What is the most common ring size for women?

US size 6 (EU 52, UK L½) is often cited as the average women's ring size in the US, corresponding to an inner diameter of about 16.5 mm. However, individual sizes vary considerably.

How do I convert between US and UK ring sizes?

US and UK ring sizes do not share a simple numeric formula. The UK system uses letters (A through Z+6) while the US uses numbers (1–15). Use the comparison table — US size 7 corresponds approximately to UK N½.

Why does ring size matter when ordering online?

Even a half-size difference (US 6 vs. 6½) changes the inner diameter by about 0.4 mm. A ring that is too tight is uncomfortable and hard to remove; too loose risks losing it. When buying online, always measure a well-fitting ring with a ruler or calipers.

Ring Size Converter — US, UK, EU, JP with mm Diameter

Ring Size Converter

Ring sizes are measured differently across regions: the US and Canada use a numbered scale (3–15), the UK and Ireland use letters (A–Z+½), and most of Europe uses the inner circumference in millimeters. All systems describe the same thing — the inner diameter of the ring — and convert with simple geometry.

How it works

inner circumference (mm) = π × inner diameter (mm)
inner diameter (mm)      = inner circumference (mm) / π

US size → inner circumference (mm):
  circumference = 36.652 + (US_size × 2.5534)

EU size (mm circumference) → US size:
  US_size = (circumference − 36.652) / 2.5534

Source: ISO 8653:2016, Jewellery — Ring-sizes.

Practical examples

Example 1 — Measuring with a string. Wrap a thin string around the base of your finger, mark where it overlaps, measure the length in mm. That length is your EU ring size (inner circumference). Divide by π to get the inner diameter.

Example 2 — US size 7 to EU. Using the table: US 7 = 54.4 mm circumference. Divide by π: 54.4 / 3.14159 = 17.32 mm inner diameter.

Example 3 — UK size L to US. UK L = EU 51.5 mm circumference. Apply the formula: (51.5 − 36.652) / 2.5534 = 5.81 → rounds to US 5¾.

Common mistakes

Measuring at the wrong time of day. Fingers swell in heat and at the end of the day. Measure in the afternoon at normal room temperature for the most representative size.
Measuring over a knuckle. If your knuckle is larger than your finger base, size to fit over the knuckle — otherwise the ring will not go on — then consult a jeweler about comfort-fit shanks.
Confusing ring circumference with ring diameter. EU sizing uses circumference (the full loop length), not diameter. A ring marked "54" is 54 mm around the inside, not 54 mm wide.
Ignoring band width. Wide bands (6 mm+) fit more snugly than the same diameter in a thin band. Size up half a US size for bands wider than 6 mm.

International and regional variations

System	Unit	Used in	Example
US / Canada	Numeric (3–15, half steps)	United States, Canada, Mexico	7
UK / Ireland / Australia	Letters A–Z + ½ steps	United Kingdom, Ireland, Australia, New Zealand, South Africa	N
EU / ISO 8653	Inner circumference in mm	Continental Europe, ISO standard	54
Japan	Numeric 1–30 (different scale)	Japan	13
Switzerland / Italy	Inner circumference in mm (same as EU)	Switzerland, Italy	54

Quick reference

US	UK	EU (mm circ.)	Japan	Inner diam. (mm)
4	H	46.8	7	14.9
5	J½	49.3	9	15.7
6	L½	51.9	12	16.5
7	N½	54.4	14	17.3
8	P½	56.9	16	18.1
9	R½	59.5	19	18.9
10	T½	62.1	21	19.8
11	V½	64.6	23	20.6
12	Y	67.2	26	21.4
13	Z+1	69.7	28	22.2

Click a row to highlight it. Measure inner circumference of an existing ring in mm to find your EU size.

US / Canada	UK / AU / ZA	EU / ISO	Japan / China	Diam. (mm)	Circum. (mm)
3	F½	44	3	14.0	44.2
3½	G½	45	4	14.4	45.1
4	H½	47	7	14.9	46.8
4½	I½	48	8	15.3	48.0
5	J½	49	10	15.7	49.3
5½	K½	51	11	16.1	50.6
6	L½	52	12	16.5	51.9
6½	M½	53	14	16.9	53.1
7	N½	54	15	17.3	54.4
7½	O½	56	17	17.7	55.7
8	P½	57	18	18.2	57.2
8½	Q½	58	20	18.5	58.3
9	R½	59	22	18.9	59.5
9½	S½	61	23	19.4	60.8
10	T½	62	25	19.8	62.1
10½	U½	63	26	20.2	63.4
11	V½	65	28	20.6	64.7
11½	W½	66	29	21.0	66.0
12	X½	67	30	21.4	67.3
12½	Y½	68	31	21.8	68.5
13	Z	70	33	22.2	69.8

Frequently Asked Questions

How do I measure my ring size at home?: Wrap a strip of paper around the base of your finger, mark where it overlaps, and measure the length in mm — this is your inner circumference. Find that value in the EU column of the table to get your ring size. Measure in the afternoon when fingers are slightly larger.
What does the EU ring size number represent?: EU ring sizes (also the ISO 8653 standard) represent the inner circumference of the ring in millimeters. EU size 52 means the ring's inner circumference is 52 mm. This is the most direct measurement-based system.
What is the most common ring size for women?: US size 6 (EU 52, UK L½) is often cited as the average women's ring size in the US, corresponding to an inner diameter of about 16.5 mm. However, individual sizes vary considerably.
How do I convert between US and UK ring sizes?: US and UK ring sizes do not share a simple numeric formula. The UK system uses letters (A through Z+6) while the US uses numbers (1–15). Use the comparison table — US size 7 corresponds approximately to UK N½.
Why does ring size matter when ordering online?: Even a half-size difference (US 6 vs. 6½) changes the inner diameter by about 0.4 mm. A ring that is too tight is uncomfortable and hard to remove; too loose risks losing it. When buying online, always measure a well-fitting ring with a ruler or calipers.