mm to Ring Size Converter
Turn an inside diameter or circumference measurement in millimeters into the closest ring size in a common sizing system.
This is handy when you have a measured ring, a printed sizing strip, or a finger measurement from a jeweler.
Calculated Result
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Run the calculation to see the closest ring size.
Quick Answer
Enter a millimeter measurement, tell the calculator whether it is circumference or diameter, and it will estimate the closest ring size from a standard chart.
How to Convert mm to Ring Size
- Measure the finger or ring in millimeters.
- Choose whether that number is a circumference or a diameter.
- Select the ring size system you need.
- Read the closest matching size and the underlying circumference.
Formula
Circumference mm = diameter mm x pi
Ring size = nearest standard size for the converted circumference
Worked Examples
Example 1: 54 mm circumference is about US size 7 and EU size 54.
Example 2: 17.3 mm diameter is about 54.3 mm circumference and roughly US size 7.
Example 3: 58 mm circumference is about US size 8.5 and UK size Q.
How to Interpret Your Results
| Result | Meaning | Action |
|---|---|---|
| Exact match | You landed on a standard chart size | Use it as-is |
| Close match | You are between two sizes | Prefer the larger size for comfort |
| Far from chart | Measurement may be off | Re-measure the finger or ring |
Frequently Asked Questions
Related Calculators
References
- OmniCalculator reference page
- Ring charts vary slightly by manufacturer and region.
- Last reviewed: March 2026.