Ring Size Converter
Convert ring sizes between US, UK and EU systems or find your size from a ring's inside diameter or finger circumference in mm.
Last reviewed by the Radiatus Cloud team
Tip: measure an existing ring's inside diameter with a ruler, or wrap a strip of paper around your finger and measure the length in mm (that's the EU/ISO size). Sizes are matched to the nearest standard size.
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Convert ring sizes across systems
Ring sizes differ by country, and buying a ring, especially as a gift, needs the right size in the right system. This converter moves between US, UK and EU ring sizes, or finds your size from a measurement.
Why ring sizing needs conversion
Ring size systems differ between countries, using different numbering or lettering, so a US size does not translate directly to a UK or EU one. The underlying measure is the finger’s circumference or diameter, which is fixed, so converting reliably means anchoring to that. This matters especially for gifts and online purchases, where getting the size wrong means an ill-fitting ring and an awkward exchange. Converting between the systems, or finding the size from a measurement, gets you the right size in whatever system the seller uses.
A calculation, not advice
It runs entirely in your browser, so nothing you enter is uploaded, keeping your figures on your own machine.
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Frequently Asked Questions
Why do ring sizes differ between countries?
Because each system numbers or letters sizes differently, so a US size does not match the UK or EU number for the same ring.
What is the underlying measure?
The finger’s circumference or diameter, which is fixed. Converting reliably anchors the systems to that measurement.
Can it find my size from a measurement?
Yes. From a finger measurement it determines the size in each system, which is useful when you do not know a starting size.
Why does this matter for gifts?
Because a ring bought as a surprise or online must be the right size, and getting the system wrong means an ill-fitting ring and an awkward exchange.
Is my data uploaded?
No. The conversion runs entirely in your browser.
Privacy & Security
Runs entirely in your browser. No data is sent to any server.
How to Use
Pick what you know (US number, UK letter, EU circumference or diameter in mm) and enter the value to see all equivalent sizes.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
Related Tools
User Agent Parser
UtilityParse a User-Agent string into browser, engine, operating system and device. Explains why UA strings are unreliable and what to use instead.
QR Code Generator
UtilityGenerate QR codes for URLs, text, Wi-Fi and contact details. Adjustable error correction and size, produced entirely in your browser.
Credit Card Validator
UtilityValidate a card number with the Luhn algorithm and identify the issuing network from its prefix. Runs locally, nothing is transmitted.