Ring Size Converter (mm ↔ US ↔ EU)
Inner diameter or circumference to US numeric and EU/ISO ring sizes with the exact linear formulas.
ISO 8653 sizes rings by inner circumference in millimetres (the EU number); US sizes are a linear scale where each whole size adds ~2.55 mm of circumference. Fingers swell warm and shrink cold by half a size — measure at the end of a normal-temperature day for the truest fit.
Formula
For general information only — not medical advice, a diagnosis or a treatment plan. Consult a qualified healthcare professional before making health, diet, medication or exercise decisions.
Inner diameter or circumference to US numeric and EU/ISO ring sizes with the exact linear formulas. The Ring Size Converter (mm ↔ US ↔ EU) is a free, private ring size converter tool — every result computes instantly in your browser with no sign-up and no data upload.
About Ring Size Converter (mm ↔ US ↔ EU)
ISO 8653 sizes rings by inner circumference in millimetres (the EU number); US sizes are a linear scale where each whole size adds ~2.55 mm of circumference. It applies EU size = circumference(mm); US size = (circumference − 36.54) ÷ 2.55. Use the Ring Size Converter (mm ↔ US ↔ EU) to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use Ring Size Converter (mm ↔ US ↔ EU)
- 1Enter your details in the Ring Size Converter (mm ↔ US ↔ EU) input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use Ring Size Converter (mm ↔ US ↔ EU)?
- ✓Instant ring size converter result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (ISO 8653:2016 — jewellery ring sizes)
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the Ring Size Converter (mm ↔ US ↔ EU) work?+
ISO 8653 sizes rings by inner circumference in millimetres (the EU number); US sizes are a linear scale where each whole size adds ~2.55 mm of circumference. The calculation uses the formula: EU size = circumference(mm); US size = (circumference − 36.54) ÷ 2.55. Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the Ring Size Converter (mm ↔ US ↔ EU) accurate, and what is it based on?+
The method is traceable to authoritative sources: ISO 8653:2016 — jewellery ring sizes. Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the Ring Size Converter (mm ↔ US ↔ EU) free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This tool is for general information only and is not medical advice. Always consult a qualified healthcare professional before making health decisions.
What can I use the Ring Size Converter (mm ↔ US ↔ EU) for?+
It's commonly used for ring size converter, ring size mm, us ring size. Inner diameter or circumference to US numeric and EU/ISO ring sizes with the exact linear formulas.
Related Health tools
Adult BMI Calculator (WHO)
Body-mass index for adults with the WHO reference bands shown neutrally, plus the substituted formula step by step.
● LiveBMI Calculator (lb & inches)
US-style BMI from pounds and inches using the ×703 conversion, with CDC adult reference ranges.
● LiveBMI Calculator for Women
BMI with reference context written for women — what the index can and cannot say about female body composition.
● Live