How to use it
Choose your input
Switch between picking a known US size or entering the inside diameter you measured in millimetres.
Read the match
The US, UK, EU, diameter and circumference for that size appear together, updating as you change the input.
Check the chart
Scan the full reference table below to compare neighbouring sizes or confirm a half-size sits between two rows.
Full size chart
Standard conversions for round band rings. Diameter is measured across the inside of the band; circumference is the inside distance all the way around. UK letters and EU numbers are the closest common equivalents.
About this converter
Ring sizing differs by country, so the same band carries a different label depending on where it was bought. This tool keeps the underlying millimetre measurement front and centre, since diameter and circumference are physical and unambiguous, while US, UK and EU labels are conventions mapped to them. When a measured diameter falls between two standard rows the nearest one is shown, which is usually close enough to order or to confirm a half size. For an exact fit, a jeweller's sizing band remains the most reliable check.
Questions
Is anything uploaded?
No. The lookup runs entirely in your browser using a built-in chart, and nothing you type is sent anywhere.
How do I measure inside diameter?
Lay a ring that fits flat and measure straight across the inside opening, edge to edge, in millimetres. Then use the "By diameter (mm)" mode to find the nearest standard size.
Why are UK and EU values approximate?
UK letters and EU numbers are rounded conventions rather than exact metric values, so they map to the nearest common label. The millimetre figures are the precise measurements to trust.