Convert a finger measurement into US, UK and EU ring sizes.
Calculated instantly in your browser.
How do you convert a finger measurement to a ring size?
Measure your finger's inner circumference or diameter in millimetres, then match it to US, UK and EU ring-size charts. For example, a 54.4 mm inner circumference is about a US size 7 (UK O). Measure at the end of the day when fingers are warm and slightly larger; sizes are approximate, so a jeweller can confirm.
Understanding your result
Measure at the end of the day when fingers are warm and slightly larger. Sizes are approximate — a jeweller can confirm.
Assumptions and limitations
Conversions are approximate and based on the measurement you enter, so an inaccurate reading gives the wrong size. Fingers change with temperature, time of day and season, and wide bands often fit tighter. It cannot account for knuckle size or band width, so a jeweller's physical sizing remains the reliable final check.
Worked example
A 54.4 mm inner circumference is about a US size 7 (UK O).
How to use this tool
- Measure the inner circumference or diameter in millimetres.
- Choose which measurement you entered.
- Press Convert.
About the Ring Size Converter
The Ring Size Converter turns a finger measurement in millimetres into US, UK and EU ring sizes, plus the inner diameter and circumference.
Who should use this tool
Shoppers buying a ring online, couples planning a surprise proposal, and anyone converting between US, UK and EU sizing. Useful for turning a measured finger or an existing ring's fit into a size before ordering from an unfamiliar retailer.
Benefits
- Converts a finger measurement into US, UK and EU sizes
- Shows the inner diameter and circumference too
- Helps you order the right size online
- Free browser tool with no sign-up
Practical use cases
- Finding a ring size before buying online
- Converting a size between US, UK and EU systems
- Checking an existing ring's inner circumference
- Planning a surprise ring for a partner
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Frequently asked questions
How do I measure ring size at home?
Wrap a thin strip of paper snugly around your finger, mark where it overlaps, and measure that length in millimetres — that’s the circumference.
When is the best time to measure?
Measure at the end of the day when your hands are warm, because fingers are smallest when cold and slightly larger when warm or after activity. Avoid measuring when your hands are very hot or swollen. Taking a couple of readings and using a mid value gives a more reliable size.
Should I size up for a wide band?
Often, yes. A wide band covers more of the finger and can feel tighter than a slim one of the same nominal size, so many people go up a size or half a size for chunky rings. If in doubt, a jeweller can confirm the right fit for a specific band width.