Ring Size Chart in cm (4.4–7.7 cm) — Circumference to US & UK

Who this is for: For anyone measuring with a cm tape measure or a cm-ruled strip — and for readers outside the US whose tape only speaks centimetres.

The full chart in centimetres — 4.4 to 7.7 cm circumference with every US and UK equivalent.

Quick answer: cm → US size = (cm × 10 − 36.5) ÷ 2.55. Landmarks: 5.0 cm = US 5¼, 5.5 cm = US 7¼, 6.0 cm = US 9¼, 6.5 cm = US 11¼, 7.0 cm = US 13¼. Measure in mm for quarter-size accuracy — one 0.1 cm slip moves the answer half a size.

Your measurement (highlight the nearest row)

Optional — the closest size row lights up so you can read across.

US	UK	Circumference	Diameter	EU / ISO	FR · IT	JP · CN
4.5	I½	4.80	1.53	48	8 · 8	8
4.5	I½	4.80	1.53	48	8 · 8	8
4.75	J	4.86	1.55	49	8.6 · 9	8
4.75	J	4.86	1.55	49	8.6 · 9	8
5	J½	4.93	1.57	49	9.3 · 9	9
5	J½	4.93	1.57	49	9.3 · 9	9
5	J½	4.93	1.57	49	9.3 · 9	9
5.25	K	4.99	1.59	50	9.9 · 10	9
5.25	K	4.99	1.59	50	9.9 · 10	9
5.5	K½	5.05	1.61	51	10.5 · 11	10
5.5	K½	5.05	1.61	51	10.5 · 11	10
5.5	K½	5.05	1.61	51	10.5 · 11	10
5.75	L	5.12	1.63	51	11.2 · 11	10
5.75	L	5.12	1.63	51	11.2 · 11	10
6	L½	5.18	1.65	52	11.8 · 12	11
6	L½	5.18	1.65	52	11.8 · 12	11
6	L½	5.18	1.65	52	11.8 · 12	11
6.25	M	5.24	1.67	52	12.4 · 12	11
6.25	M	5.24	1.67	52	12.4 · 12	11
6.5	M½	5.31	1.69	53	13.1 · 13	12
6.5	M½	5.31	1.69	53	13.1 · 13	12
6.5	M½	5.31	1.69	53	13.1 · 13	12
6.75	N	5.37	1.71	54	13.7 · 14	12
6.75	N	5.37	1.71	54	13.7 · 14	12
7	N½	5.44	1.73	54	14.3 · 14	13
7	N½	5.44	1.73	54	14.3 · 14	13
7	N½	5.44	1.73	54	14.3 · 14	13
7.25	O	5.50	1.75	55	15 · 15	14
7.25	O	5.50	1.75	55	15 · 15	14
7.5	O½	5.56	1.77	56	15.6 · 16	14
7.5	O½	5.56	1.77	56	15.6 · 16	14
7.5	O½	5.56	1.77	56	15.6 · 16	14
7.75	P	5.63	1.79	56	16.3 · 16	15

Every row derives from one formula — circumference = 2.55 × US size + 36.5 — so columns cannot contradict each other.

Core facts

5.0 cm	US 5¼ · UK K
5.5 cm	US 7¼ · UK O
6.0 cm	US 9¼ · UK S
6.5 cm	US 11¼ · UK W
7.0 cm	US 13¼ · UK Z+1
Precision	0.1 cm ≈ 0.39 US size

How do I use a ring size chart in cm?

Measure your finger's circumference with a cm tape (or a paper strip checked against a ruler), then read the row. One centimetre of circumference spans about 0.39 US sizes, so quarter-size precision needs millimetres — that's why the chart shows cm to two decimals. The formula: US size = (circumference in mm − 36.5) ÷ 2.55.

Common uses

Convert a cm tape reading straight to US/UK size without mental math
Check whether 5.5 cm, 6 cm or 7 cm fingers land where blogs claim
Print a cm-column chart for a partner sizing in a metric country
Sanity-check an EU seller's cm-based listing against US sizes

Frequently Asked Questions

What ring size is 6 cm?

6 cm = 60 mm of circumference → (60 − 36.5) ÷ 2.55 = US 9¼ (UK S, EU 60). If a chart tells you 6 cm is a US 7, it scaled the units wrong.

What ring size is 5.5 cm?

5.5 cm = 55 mm → (55 − 36.5) ÷ 2.55 = US 7¼ (UK O, EU 55). Right in the average women's band.

What ring size is 7 cm?

7 cm = 70 mm → US 13¼ (UK Z+1, EU 70). This is the measurement blogs most often get wrong — many print US 9, which is actually 59.5 mm.

Why do cm charts need two decimals?

Because 0.1 cm = 1 mm = about 0.39 US sizes. A chart rounded to whole centimetres can be off by two full sizes — always measure to the millimetre.

More ring size charts

Ring Size Chart

Full US 3–16 chart with UK, EU, French, German and Japanese columns — filter, highlight and print.

Men's Ring Size Chart

US 8–15 chart for men, with the wide-band and knuckle adjustments that move men's sizes most.

Printable Ring Size Chart

A print-ready ring sizer with a credit-card calibration box — print, cut, wrap, read.

Ring Size Conversion Tool

Convert any size between US, UK, EU, French, German, Japanese and Chinese systems — both directions.

Related guides

How to Measure Ring SizeFour accurate home methods — existing ring, paper strip, calibrated printable, and the gift secret-weapon.
The Complete Ring Size GuideEvery sizing system explained, quarter sizes, width and knuckle rules, and what resizing costs.
7 cm in Ring SizeExactly what 7 cm of circumference converts to — with the math many blogs get wrong.
Average Ring SizeWhat the average man and woman wear, how build shifts it, and how to guess well for gifts.
Ring Size 8Everything about US size 8: exact millimetres, international equivalents, and who wears it.