Measure Ring Size

General calculator

Ring size calculator

One calculator for every number you might have: a diameter from a ring, a circumference from a paper strip, or a size from another chart. Pick what you measured, pick the unit, and the result updates as you type.

General ring size calculator

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

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.

How to use this calculator

  1. Choose what you measured

    Inner diameter if you measured across a ring; circumference if you measured around a finger or a strip. The two are linked by circumference = π × diameter, and the calculator converts between them without rounding the intermediate value.

  2. Choose the unit you actually used

    Millimetres, centimetres, or inches. The number is converted to millimetres internally for lookup, and the conversion is exact (1 inch = 25.4 mm, 1 cm = 10 mm) — no approximate unit factors.

  3. Read all three systems, then highlight yours

    US, UK (approx.) and EU are shown together, because they are separate ladders for the same measurement. Use the country selector to highlight the system you are ordering in.

Why this calculator does not use a size formula

Some calculators invent a universal formula (for example, a straight line from circumference to US size). This one does not: it looks your measurement up in the validated reference table, US 3–13.5, and reports the nearest row — or flags that you sit between two rows. That is why a US size, a UK letter and an EU number for the same measurement can look unrelated: they are labels from different systems, not conversions of each other.

Why you can trust this result

  • Calibration uses a standard bank card (85.6 mm wide, ISO/IEC 7810 ID-1) — a physical reference, not a guess about your screen.
  • Your measurement is calculated in your browser and is not sent to a server. There is no account, and analytics runs only if you consent to it.
  • Results are guidance, not a guarantee. For an expensive or hard-to-resize ring, confirm with a professional fitting.

Related guides

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