Tool
Ring size converter
Convert between US, UK, European, Japanese and millimetre sizes — starting from the only measurement that is not a convention.
The size as it was given to you.
Inner diameter
17.32 mm
The only measurement here that is not a convention. Everything below is this number wearing a different label.
US / Canada
7
UK / Australia
N½
Europe (ISO)
54.4
= circumference in mm
Japan / China
14
Charts disagree, and this one is no exception
The European size is the circumference in millimetres, which is defined and unarguable. The US, UK and Japanese scales are conventions, and makers round them differently — you will find charts that put this measurement half a size either way. If a ring is being cut or resized rather than tried on, give the workshop the millimetres, not the letter.
What actually affects the fit
A finger is not one size all day
It swells in heat and late in the day, and shrinks in cold and first thing in the morning — the swing across a day is commonly close to half a size. Measure at the end of the day, at normal room temperature, and measure more than once.
A wide band needs a bigger size
A band over about 6 mm wide sits across more of the finger and feels tighter at the same measurement. Going up a quarter to a half size is the usual allowance.
The knuckle is the real constraint
If the knuckle is much wider than the base of the finger, size to get the ring over the knuckle and expect it to spin. Sizing beads or a fitted bar fix the spinning without fighting the knuckle.
String and paper measurements read small
Both compress and neither slides over a knuckle, so they tend to under-read. Treat a string measurement as a starting point and confirm with a proper sizer before anything is cut.
Not every ring can be resized
Full eternity bands, tension settings, and most titanium, tungsten and ceramic rings cannot be sized at all. On those, the measurement has to be right the first time.
The full chart
US 3 to 14, with every scale alongside. The diameter column is computed from the US standard — size 0 is 0.458 inch across and each size adds 0.032 inch — and the European column is simply the circumference, because that is what an ISO size is.
| US | UK / AU | Europe | Japan | Diameter | Circumference |
|---|---|---|---|---|---|
| 3 | F½ | 44.2 | 4 | 14.07 mm | 44.2 mm |
| 3.5 | G½ | 45.5 | 5 | 14.48 mm | 45.5 mm |
| 4 | H½ | 46.8 | 7 | 14.88 mm | 46.8 mm |
| 4.5 | I½ | 48 | 8 | 15.29 mm | 48.0 mm |
| 5 | J½ | 49.3 | 9 | 15.70 mm | 49.3 mm |
| 5.5 | K½ | 50.6 | 10 | 16.10 mm | 50.6 mm |
| 6 | L½ | 51.9 | 12 | 16.51 mm | 51.9 mm |
| 6.5 | M½ | 53.1 | 13 | 16.92 mm | 53.1 mm |
| 7 | N½ | 54.4 | 14 | 17.32 mm | 54.4 mm |
| 7.5 | O½ | 55.7 | 15 | 17.73 mm | 55.7 mm |
| 8 | P½ | 57 | 16 | 18.14 mm | 57.0 mm |
| 8.5 | Q½ | 58.3 | 18 | 18.54 mm | 58.3 mm |
| 9 | R½ | 59.5 | 19 | 18.95 mm | 59.5 mm |
| 9.5 | S½ | 60.8 | 20 | 19.35 mm | 60.8 mm |
| 10 | T½ | 62.1 | 21 | 19.76 mm | 62.1 mm |
| 10.5 | U½ | 63.4 | 23 | 20.17 mm | 63.4 mm |
| 11 | V½ | 64.6 | 24 | 20.57 mm | 64.6 mm |
| 11.5 | W½ | 65.9 | 25 | 20.98 mm | 65.9 mm |
| 12 | X½ | 67.2 | 26 | 21.39 mm | 67.2 mm |
| 12.5 | Y½ | 68.5 | 27 | 21.79 mm | 68.5 mm |
| 13 | Z½ | 69.7 | 29 | 22.20 mm | 69.7 mm |
| 13.5 | Z+1½ | 71 | 30 | 22.61 mm | 71.0 mm |
| 14 | Z+2½ | 72.3 | 31 | 23.01 mm | 72.3 mm |
Next
Weigh it, pick the karat, and see the value of the metal at the live gold price — then what a buyer is likely to hand over, which is a different number.
Sterling, coin, Britannia and fine silver at the live silver price — including why small silver items are often worth less than the trouble of selling them.
PT950, PT900 and PD950 at live prices. Both metals are denser than gold, which is why the weight surprises people.