Ring Size Converter
Convert Ring Size values quickly with a focused online tool.
This ring size converter translates a ring size between US, UK, and EU sizing systems, or converts a measured finger circumference or diameter into a ring size - useful for buying jewelry from international retailers.
Enter your ring size (or finger measurement), and the calculator returns the equivalent sizes across systems.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| Finger circumference 54.4 mm | US size ≈7 | Per standard ring sizing charts, 54.4 mm internal circumference corresponds to approximately US size 7. |
| Finger circumference 62.1 mm | US size ≈10 | Per standard ring sizing charts, 62.1 mm internal circumference corresponds to approximately US size 10. |
Why Ring Sizing Systems Differ
US ring sizes use a numeric scale (commonly 3-13, often with half sizes), UK sizes use a letter scale (A-Z), and many EU countries measure ring size directly by internal circumference in millimeters - since these are fundamentally different measurement approaches, an accurate conversion requires either a conversion chart or converting through the underlying physical measurement.
Measuring Finger Circumference for an Accurate Size
The most reliable ring sizing method measures a string or strip wrapped snugly around the finger's base, then converts that circumference in millimeters to a ring size - this avoids ambiguity from converting between regional size charts and tends to be more accurate than working from an existing ring's noted size alone.
How to Use the Ring Size Converter
- Open the Ring Size Converter and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the ring size converter works.
Frequently Asked Questions
How do US and UK ring sizes compare?
They use entirely different scales - US uses numbers (roughly 3-13) while UK uses letters (A-Z) - so converting between them requires a conversion chart based on internal circumference rather than a simple numeric offset.
How do I measure my ring size at home?
Wrap a strip of paper or string snugly around the base of your finger, mark where it overlaps, measure that length in millimeters, and use a ring size chart to match that circumference to a size.
Does finger size change throughout the day?
Yes - fingers can swell slightly with temperature, activity, and time of day, so many jewelers recommend measuring at room temperature, later in the day, when fingers tend to be at their most typical size.
How do I use this ring size converter?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Ring Size Converter calculate?
Convert Ring Size values quickly with a focused online tool. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this ring size use?
The formula is: US Size ≈ f(Internal Circumference in mm) — per jewelry industry sizing charts. Unlike the US numeric scale, the UK ring sizing system uses letters (A through Z, with half sizes), a convention that developed independently within the British jewelry trade - since both systems ultimately describe the same physical internal circumference, converting between them (or measuring a new ring size from scratch) is most reliably done by working through that shared underlying millimeter measurement rather than a direct letter-to-number formula.
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Last updated: September 27, 2026.