Free CM to Ring Size Converter

What This Centimeter to Ring Size Converter Does

The CM to Ring Size Converter is a free online finger ring size calculator that helps you determine your correct ring size using nothing more than a strip of paper and a ruler marked in centimeters. Whether you’re buying a gift or checking your own fit, this tool supports international ring size conversion across US & Canada, UK & Australia, France, Germany, Japan, and Switzerland. An accurate size prevents rings from being too tight (which can restrict circulation) or too loose (risking loss during everyday wear).

How to Measure Your Finger

You don’t need any special equipment. Cut a thin strip of paper about 15 cm long and 0.5 cm wide. Wrap it around the finger you want to size — make sure it passes over the knuckle where the ring will sit. Use a pen to mark where the end of the strip meets the rest of the paper. Then lay the strip flat against a ruler and read the length in centimeters. That number is your finger’s inner circumference.

Enter that circumference value into the centimeter to ring size calculator. For example, a measurement of 5.6 cm returns a US & Canada size of 7 3/4 and a UK & Australia size of P 1/2. The tool can also accept an inside diameter: if you have a ring that fits well, measure its inner diameter and input that instead. (The circumference equals $\pi \times \text{diameter}$.)

International Ring Size Conversion Chart

The table below provides a quick ring size chart in centimeters, showing the relationship between the inner diameter (cm), inner circumference (cm), and the equivalent sizes in the major international sizing systems. Use it to cross‑reference any of the standards.

Inner Diameter (cm)	Inner Circumference (cm)	US & Canada	UK & Australia	France	Germany	Japan	Switzerland
1.153	3.622	0	–	–	–	–	–
1.195	3.754	–	1/2	–	–	–	–
1.237	3.886	–	1	–	1	–	–
1.278	4.015	–	1 1/2	–	–	–	–
1.321	4.150	2	D	41 1/2	13 1/2	2	1 1/2
1.361	4.276	2 1/2	E	42 3/4	13 3/4	3	2 3/4
1.405	4.414	3	F	44	14	4	–
1.436	4.511	–	G	45 1/4	–	5	5 1/4
1.445	4.540	–	G 1/4	–	–	14 1/2	–
1.456	4.574	–	G 1/2	–	–	6	–
1.465	4.602	–	H	46 1/2	–	6 1/2	–
1.486	4.668	4	H 1/2	–	15	7	–
1.504	4.725	4 1/4	I	47 3/4	–	7 3/4	–
1.527	4.797	4 1/2	I 1/2	–	15 1/4	8	–
1.540	4.838	–	J	49	15 1/2	–	9
1.570	4.932	5	J 1/2	–	15 3/4	9	–
1.580	4.964	5 1/8	K	50	–	10	–
1.600	5.027	–	K 1/2	–	–	10	–
1.610	5.058	–	L	51 3/4	16	–	11 3/4
1.651	5.187	6	M	52 3/4	16 1/2	12	12 3/4
1.692	5.316	6 1/2	N	54	17	13	14
1.735	5.451	7	O	55 1/4	17 1/4	14	15 1/4
1.775	5.576	7 1/2	P	56 1/2	17 3/4	15	16 1/2
1.819	5.715	8	Q	57 3/4	18	16	17 3/4
1.853	5.821	8 1/2	Q 3/4	–	18 1/2	17	–
1.861	5.847	8 5/8	R	59	–	19	–
1.889	5.934	9	R 3/4	–	19	18	–
1.910	6.000	9 1/8	S	60 1/4	–	–	20 1/4
1.941	6.098	9 1/2	S 3/4	–	19 1/2	19	–
1.951	6.129	9 5/8	T	61 1/2	–	–	21 1/2
1.984	6.233	10	T 1/2	–	–	20	–
2.002	6.289	10 1/4	U	62 3/4	–	21	22 3/4
2.020	6.346	10 1/2	U 1/2	–	20 1/4	22	–
2.032	6.384	10 5/8	V	63	–	–	23 3/4
2.068	6.497	11	V 1/2	–	20 3/4	23	–
2.076	6.522	11 1/8	W	65	–	–	25
2.108	6.622	11 1/2	W 3/4	–	21	24	–
2.118	6.654	11 5/8	–	66 1/4	–	–	26 1/4
2.149	6.751	12	Y	67 1/2	21 1/4	25	27 1/2
2.189	6.877	12 1/2	Z	68 3/4	21 3/4	26	28 3/4
2.233	7.015	13	Z+1	–	22	27	–

Note: A dash (“–”) means that particular size does not have a direct equivalent in that system. The table follows the raw data of the converter, so some entries may appear numeric or fractional as sourced.

Getting the Most from the Converter

Besides entering either circumference or diameter, you can click the “ring size equivalents” section of the tool to browse neighboring sizes. For instance, if 7 3/4 (US) does not have a direct match in another system, checking size 8 (US) will show its equivalents. This free ring size calculator identifies the closest matches across all supported standards, making centimeter to ring size conversions both quick and reliable. Keep this ring size chart CM handy for offline reference, and always verify your fit before purchasing.