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US to EU Ring Size Converter

Convert ring sizes between the US, UK, EU/ISO and Japanese systems, or start from a measured diameter or circumference in millimetres.

How to measure at home

No ring at hand: wrap a thin strip of paper or a thread snugly around the base of the finger, mark where it overlaps and measure the length in mm — that is the circumference. Fingers swell during the day, so measure in the evening at room temperature.

With a ring that fits: measure the inner diameter of the ring in mm from edge to edge across the centre, then convert from “Inner diameter, mm”. Pick a ring worn on the same finger of the same hand.

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Reading the size
Matching the ISO 8653 table
Building the conversion

Result

This page opens the ring size converter with the direction already set: from the US & Canada scale to the European ISO size. Type an American size such as 7 or 6.5, press the button, and you get the EU size — which is simply the inner circumference in millimetres — together with the matching UK letter, Japanese size and inner diameter.

The two scales are built differently: US sizes grow in quarter and half steps of about 0.8 mm of diameter per full size, while the EU/ISO 8653 size is the circumference itself, so a US 7 corresponds to roughly EU 54.4 and a US 6 to about EU 52. Because the systems do not align on round numbers, a conversion table beats mental math every time.

This direction is most useful when you know a size from an American brand and want to order from a European jeweller. If the result lands between two European sizes in the shop's catalogue, take the larger one — a slightly loose ring can be worn, a tight one cannot.

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Accepted Formats & Rules

  • ISO 8653 based conversion table with 44 standard sizes.
  • Accepts UK letter sizes including halves, like M or M½.
  • Millimetre inputs are interpolated between table rows for an exact match.

Key Benefits

✓ Convert between five sizing systems and raw millimetre measurements in one place.
✓ See the full matching row at once — US, UK, EU/ISO, Japan, diameter and circumference.
✓ Includes simple instructions for measuring your finger or an existing ring at home.

Use Cases

  • • Convert a ring size from an American online store to the EU size your local jeweller uses.
  • • Find your own size by measuring an existing ring's inner diameter or your finger's circumference.
  • • Check a UK letter size like M½ against the US, European and Japanese scales before ordering a gift.