Ring Size Converter — JP (号), US, UK, EU/ISO & mm
Convert ring sizes between Japanese 号, US, UK letters and EU/ISO circumference, or start from a measured inner diameter or circumference in mm — nearest match plus a full chart.
🔒 Runs entirely in your browser. Your input and output are never sent to a server or stored — fully private.
Sizes are standards-based approximations and makers vary — wide bands fit tighter, and fingers change size during the day. When possible, have your finger measured or check the seller’s own size guide. EU/ISO size is the inner circumference in millimetres.
Full chart
| JP (号) | US | UK | EU / ISO (mm) | Inner diameter (mm) |
|---|
About this tool
A ring bought abroad, an engagement surprise, an online order from a Japanese jeweller — ring sizes come in incompatible systems, and this converter bridges them all: Japanese 号 numbers, US/Canada numeric sizes, UK/Australia letters, and the EU/ISO scale based on inner circumference in millimetres, alongside the inner diameter. Enter a size in any system, or a measured diameter or circumference, and read off the rest — a US 7 is a JP 14号, roughly EU 54. Measuring tips are included. The tables live in the page and everything runs in your browser; nothing you enter is sent anywhere.
Frequently asked questions
How do I measure my ring size accurately at home?
The most reliable way is to measure a ring that already fits that finger: lay it on a ruler and read the inner diameter in millimetres, then enter it here. Failing that, wrap a strip of paper or thread snugly around the finger's base, mark the overlap and measure the length — that is the circumference. Fingers swell and shrink: measure in the evening, at normal room temperature, never right after exercise or in the cold, and take two or three readings on different days.
Will the converted size always fit?
Treat it as a standards-based starting point, not a guarantee. Ring sizing varies between makers and countries: some jewellers round to half sizes, letter systems are spaced differently from numeric ones, and the ring's design matters — a wide band fits noticeably tighter than a thin one, so many jewellers recommend going up half a size for bands over 6 mm. For an expensive piece, confirm against the jeweller's own size chart or get sized in store; resizing is easier to avoid than to fix.
I'm between two sizes — which should I choose?
Usually the larger one. A ring should slide over the knuckle with a little resistance and sit snugly without leaving deep marks; too tight is more uncomfortable — and harder to remove — than slightly loose. If your knuckle is clearly wider than the base of your finger, size for the knuckle and accept a little play at the base. Also remember that Japanese 号 steps are finer than US whole sizes, so the "between" gap is often smaller than it looks.