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.
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About this tool
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.
Example. US size 7 maps to inner diameter 17.32 mm, circumference 54.4 mm, UK N½, and Japanese size 14.
Limit. Circumferences outside the published table, roughly the span around US sizes covered by the ISO rows, are rejected.