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Ring Diameter to Size Calculator
Enter inside ring diameter in millimeters and estimate the closest common US, UK, EU, and Japan ring size.
Target query: ring diameter to size calculator. Use this as a sizing reference, not a seller-specific guarantee.
Conversion tool
Enter the size or measurement you already have. The page returns the closest common chart match across US, UK, EU, Japan, circumference, and diameter.
Result
Select a size to begin
- US
- --
- UK
- --
- EU
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- Japan
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- Circumference
- --
- Diameter
- --
Converted values will appear here.
How diameter maps to ring size
Inside diameter is converted to circumference with circumference = diameter x pi, then matched to the closest common chart row.
Example
A 17.31 mm inside diameter is close to a 54.40 mm circumference, which maps near US 7 and UK N in this reference chart.
Reference chart
Ring size conversion table
Use the table for a fast scan, then confirm with the converter and a seller-specific chart when buying jewelry.
| US | UK | EU | Japan | Circumference mm | Diameter mm |
|---|
FAQ
Is this conversion exact?
No. Ring size systems use different reference points, so a conversion is best read as a close chart match.
Why can seller charts differ?
Band width, comfort-fit design, regional chart rounding, and brand tolerances can change the recommended size.
Should I size up or down?
Do not size up or down from a chart alone. Measure at a normal finger temperature and check the seller's return or resizing policy.