Ring Size Finder
Convert a ring's inside diameter or circumference (mm or inches) into US, UK and EU ring sizes.
This maps your measurement to the nearest standard published ring size. Always check the specific jeweler or retailer's own chart before buying — fingers change size slightly with temperature and time of day, and a wide band fits differently than a thin one at the same circumference.
Starting from a real measurement instead of a remembered size
Ring sizing is one of the more standardized conversions on this site precisely because all three major systems — US numbers, UK letters, and EU circumference-in-millimetres — ultimately map to the same real internal measurement of the ring. This tool works from that measurement directly: enter a diameter or circumference in millimetres or inches, and get the corresponding US, UK, and EU sizes at once, rather than converting a size you're only approximately sure of from memory.
Diameter and circumference are different figures — this tool handles both
Pick the correct field before you type a number in: this tool keeps diameter and circumference as two separate inputs rather than one ambiguous 'ring measurement' box, specifically because mixing the two up — feeding a circumference into a diameter field or the reverse — is the single most common manual-conversion mistake this tool is built to remove.
Where your measurement comes from affects how much to trust it
A measurement taken with a proper jeweler's ring mandrel is the most reliable input this tool can work with. A measurement derived from wrapping a strip of paper around your finger and marking the overlap, a common at-home method, is a reasonable estimate but carries more built-in error — worth treating the output as a helpful starting point rather than a guaranteed exact size if that's how you arrived at your figure. An existing ring that's been worn and stretched slightly over years is also a less precise source than a fresh direct measurement.
The output is a conversion, not a guarantee against the variables real fingers have
Whatever measurement you enter, the US, UK, and EU sizes this tool returns describe that specific circumference or diameter translated across systems — they can't account for the fact that fingers swell and shrink meaningfully with temperature, time of day, salt intake, and activity level, sometimes enough to shift which size actually feels comfortable at different points in the same day. They also can't tell you how much to size up for a notably wide band, which sits against more of the finger's surface than a thin one at the identical circumference.
Built from the same standardized conversion tables as the rest of the site
This tool's US-UK-EU mapping uses the same closely standardized ring-sizing relationships covered on this site's dedicated ring-size conversion pages — it's a faster way to reach the same result when you already have a millimetre or inch measurement in hand rather than a size number you're converting from a different system.
Frequently asked questions
How do I know whether my jeweler gave me a diameter or a circumference figure?
Check the receipt or sizing slip for the word itself, or ask directly — this tool keeps the two as separate input fields rather than guessing, since entering one type into the other field's box produces a confidently wrong answer.
Is a measurement from a paper-strip method as reliable as a jeweler's mandrel?
Not quite — a DIY paper-strip measurement gives a reasonable estimate but carries more margin for error than a professional mandrel measurement, so treat the tool's output as a helpful starting point if that's your source.
Does this tool use the same conversion logic as the site's ring-size conversion pages?
Yes — it applies the same closely standardized US-UK-EU relationships, just starting from a millimetre or inch measurement you already have rather than a size number from a different system.
I entered a number and got a result that's obviously wrong (a tiny or huge ring size) — what happened?
The most common cause is mixing up millimetres and inches in the input field, or accidentally entering a circumference into the diameter field (or the reverse) — double-check both the unit and the field before assuming the underlying conversion is at fault.
Can I enter a size I already know (like a US number) to work backward to a millimetre figure?
This tool is built to go from a raw measurement to a size, not the reverse — for converting a known size number between systems, the dedicated ring-size conversion pages handle that direction directly.