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UK to US 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 set to translate British letter sizes into American numbers. Type a letter such as M, P½ or even Z+1 and the converter returns the closest US size along with the EU/ISO size, the Japanese size and the exact diameter and circumference in millimetres.

The UK scale — also used in Ireland, Australia and New Zealand — runs from A upward in letters and half letters, each half letter adding roughly 0.6 mm of circumference. Common anchors: L½ is close to US 6, N½ to US 7, and P½ to US 8. Half sizes are accepted in several spellings: M½, M 1/2 or M.5 all work.

The letter-to-number mapping is the least exact of all ring conversions, and published charts genuinely disagree by up to half a size. The tool shows the closest standard row so you can sanity-check against the millimetre values — and when in doubt between two US sizes, order the larger.

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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.