cm to Ring Size Converter
Measure a finger in centimeters and estimate the closest ring size in US, UK, and EU charts.
Use the calculator for a quick approximation before checking a jeweler's final sizing tool.
Result
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Run the calculation to see the nearest ring size.
Quick Answer
A ring measurement in centimeters can be converted to millimeters, then matched to the nearest common ring chart entry.
How to Use It
- Measure the finger circumference or diameter in centimeters.
- Enter the value into the calculator.
- Add a small allowance if you want a looser fit.
- Click Calculate to see the nearest US, UK, and EU sizes.
Formula
Circumference in mm = centimeters x 10
Diameter in mm = circumference in mm / pi
Worked Examples
Example 1: 5.6 cm maps to about EU 56, US 7.75, and UK P 1/2.
Example 2: A 1.8 cm diameter gives a circumference close to 56.5 mm before allowance.
Example 3: Adding 0.5 mm allowance can move the answer to the next nearest chart size.
How to Interpret Your Results
| Output | Meaning | Action |
|---|---|---|
| US size | The closest common American ring size. | Compare with your jeweler's sizing ring. |
| UK size | The closest common British ring size. | Use the same chart if you buy from a UK seller. |
| EU size | The closest circumference-based European size. | Check whether a half-size adjustment is needed. |
Frequently Asked Questions
Yes. The ring has to pass over the knuckle, so the size should be comfortable enough to slide on without being loose on the finger.
Sizing systems grew up in different markets, so the numbering and half-size steps do not line up perfectly across countries.
Yes, but compare the result with the seller's own chart first because some brands use slightly different ring standards.
Related Calculators
References
- OmniCalculator reference page
- The calculator matches the converted circumference to the nearest common ring chart entry.
- Last reviewed: March 2026.