Ring size
Convert between UK, US, EU and Japanese sizes, and read the inside diameter in millimetres.
— · 54.4 mm around · Sterling silver 925
| UK | Ø mm | Around | US | EU | JP |
|---|---|---|---|---|---|
| G | 14.32 | 45.0 | 3½ | 45 | 5 |
| H | 14.72 | 46.2 | 4 | 46 | 6 |
| I | 15.12 | 47.5 | 4½ | 48 | 7 |
| J | 15.52 | 48.8 | 4¾ | 49 | 8 |
| K | 15.92 | 50.0 | 5¼ | 50 | 10 |
| L | 16.31 | 51.2 | 5¾ | 51 | 11 |
| M | 16.71 | 52.5 | 6¼ | 52 | 12 |
| N | 17.11 | 53.8 | 6¾ | 54 | 13 |
| N½ | 17.31 | 54.4 | 7 | 54 | 14 |
| O | 17.51 | 55.0 | 7¼ | 55 | 15 |
| P | 17.90 | 56.2 | 7¾ | 56 | 16 |
| Q | 18.30 | 57.5 | 8¼ | 57 | 17 |
| R | 18.70 | 58.7 | 8¾ | 59 | 18 |
| S | 19.10 | 60.0 | 9¼ | 60 | 19 |
| T | 19.49 | 61.2 | 9¾ | 61 | 20 |
| U | 19.89 | 62.5 | 10¼ | 62 | 22 |
| V | 20.29 | 63.7 | 10¾ | 64 | 23 |
| W | 20.68 | 65.0 | 11¼ | 65 | 24 |
| X | 21.08 | 66.2 | 11¾ | 66 | 25 |
| Y | 21.48 | 67.5 | 12¼ | 67 | 26 |
| Z | 21.88 | 68.7 | 12¾ | 69 | 27 |
Ring size conversion
A UK ring size N½ is a US size 7, an EU size 54 and a Japanese size 14. All four name a ring 17.31 mm across the inside and 54.4 mm around. UK and Australian sizes are letters, US and Canadian sizes are numbers, and the EU number is the inside circumference in millimetres rounded to the nearest whole one, which is why two neighbouring UK letters can share it.
When two charts disagree, work from the millimetres. The letters and numbers are labels, and manufacturers round them differently.
How to measure a ring size
A ring gauge is the reliable method. Slide the sizes on until one passes the knuckle with slight resistance and comes off with slight resistance too. Measure at the end of the day when fingers are largest, and when hands are warm, because cold fingers can read a full size small.
Measuring a ring you already own
Put it on a mandrel and read the line where it stops, or measure the inside diameter across the middle with digital callipers and find that figure in the table above. Measure the inside of the band, never the outside.
Common questions
What is a UK N½ in US sizes?
A UK N½ is a US 7. The inside diameter is 17.31 mm and the inside circumference is 54.4 mm. In the EU system it is 54 and in Japan it is size 14.
How do I convert ring size to millimetres?
Look up the inside diameter for the letter or number in the table above, then multiply by pi if you need the circumference instead. A UK K is 15.92 mm across and 50.0 mm around.
Are UK and US ring sizes the same?
No. The UK uses letters and the US uses numbers, and they do not line up evenly. Roughly, each US whole size spans about two UK letters, so conversions often land on a UK half size.
What is a half size in ring measurement?
A UK half size sits between two letters and is written with a half symbol, so N½ falls between N and O. It is about 0.2 mm of diameter, which is a noticeable difference on a narrow band.
Should a wide ring be a bigger size?
Yes. Anything above about 6 mm wide grips more of the finger and feels tighter. Going up a half size is the usual allowance for a wide band.
Can any ring be resized?
Plain bands resize up or down by a size or two without much trouble. Rings set with stones all the way round, or with engraving, channel settings or an inlay, often cannot be resized without remaking the piece.