Measure Ring Size

Circumference calculator

Ring circumference calculator

You have a circumference number — from a jeweller, another chart, or a measurement of a ring. Type it in and convert it to internal diameter and size equivalents.

Ring circumference calculator

Decimal numbers are welcome. Use a dot for decimals, for example 16.5.

What you measured

Circumference

Changing the unit reinterprets the number you typed in the new unit — it does not convert it. Re-enter the number if you measured in a different unit.

Try an example

Highlight my country's size

Enter a measurement to see your size.

Formulas: circumference = π × diameter; diameter = circumference ÷ π. Matching uses your full, unrounded value; displayed diameter is rounded to 2 decimal places and circumference to 1 decimal place.

Where a ring circumference number comes from

  1. From a jeweller or a chart

    EU sizes are circumferences by definition (EU 52 means about 52 mm around the inside), so an EU size you already own is a circumference you can type straight in.

  2. From a thin strip inside the ring

    Press a thin, non-stretchy strip against the inside of the ring, mark where it meets itself, then lay it flat against a ruler. That length is the inner circumference.

  3. Not from around a finger

    A circumference measured around a finger is a finger measurement, not a ring circumference — the two are close but not identical, because a finger is not a perfect circle. For a finger, use the finger calculator instead.

Illustration of measuring around a ring or finger to get its circumference
Illustration only — not a sizing template. Measure a real circumference, then convert it in the calculator above.

How the conversion works

Diameter = circumference ÷ π, with no intermediate rounding: your full circumference value is divided by π, and only the displayed diameter is rounded (to 2 decimal places). The diameter is then looked up in the validated reference table, so the size you get is the nearest table row for your measurement — or a between-sizes flag if you sit between two rows — not a value from a universal size formula.

Related guides

We use simple cookies to see which tools people use, so we can make this site better. We never see your measurements or personal details, and there are no ads. You can say no and still use everything.