Ring Size Converter
Convert ring sizes: US, UK, EU, JP.
Ring sizing is a mess of competing systems — US numbers, UK letters, EU millimeters of inner circumference.
How to use
- Enter your known size and its system.
- Click Convert for all four systems.
- When between sizes, jewelers recommend sizing up.
About this tool
This converter maps between them via circumference, the one true measurement.
Sizing varies by band width and brand; a jeweler’s measurement is the gold standard.
How it works
Ring size is just the inner circumference of the band in disguise. US sizes run almost linearly: each full size adds about 2.55 mm of circumference (0.81 mm of diameter). A US 6, for example, is 51.9 mm around and 16.5 mm across.
Other systems encode the same measurement differently. The UK uses letters (L, M, N…), the EU/ISO system states the circumference in millimetres directly (EU 52 = 52 mm), and Japan uses its own numbering. Convert between them with the table — or measure in millimetres and read across.
Measure at the end of the day, when fingers are at their largest, and size for the knuckle: the ring should slide over it with slight resistance. Between sizes, jewellers usually recommend going up.
Worked examples
String measurement: A strip of paper around the finger measures 54 mm. Reading across: about US 7, UK N, EU 54.
US to UK: You know you are a US 8 (57.0 mm circumference, 18.1 mm diameter). That is roughly a UK P and an EU 57.
Quick reference
| US | Diameter (mm) | Circ. (mm) | UK | EU |
|---|---|---|---|---|
| 4 | 14.9 | 46.8 | H | 47 |
| 5 | 15.7 | 49.3 | J | 49 |
| 6 | 16.5 | 51.9 | L | 52 |
| 7 | 17.3 | 54.4 | N | 54 |
| 8 | 18.1 | 57.0 | P | 57 |
| 9 | 19.0 | 59.5 | R | 60 |
| 10 | 19.8 | 62.1 | T | 62 |
| 11 | 20.6 | 64.6 | V | 65 |
| 12 | 21.4 | 67.2 | X | 67 |
Frequently asked questions
Should I size up or down?
Up — especially for wide bands, which fit tighter.
Why measure in the evening?
Fingers are largest late in the day; cold mornings shrink them.
Is my input stored?
No.
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