Ring Size Converter
Type a size on any scale and the converter gives the nearest size on every other scale, with the inner diameter and circumference in mm and how far each nearest size is from exact. US 7, for example, is 54.4 mm around: UK N½, EU 54.5, Japan 14.
Your size on every scale
UK N½
US 7 on the other scales
- US / Canada 7 (exact)
- UK / Australia N½ (exact)
- EU / ISO 54.5 (exact)
- Japan 14 (exact)
- Inner diameter 17.32 mm (0.682 in)
- Inner circumference 54.4 mm (2.14 in)
| US | Diameter mm | Circumference mm | UK | EU / ISO | Japan |
|---|---|---|---|---|---|
| 3 | 14.07 | 44.2 | F½ | 44 | 4 |
| 3½ | 14.47 | 45.5 | G½ | 45.5 | 5 |
| 4 | 14.88 | 46.8 | H½ | 47 | 7 |
| 4½ | 15.29 | 48 | I½ | 48 | 8 |
| 5 | 15.69 | 49.3 | J½ | 49.5 | 9 |
| 5½ | 16.1 | 50.6 | K½ | 50.5 | 10 |
| 6 | 16.51 | 51.9 | L½ | 52 | 12 |
| 6½ | 16.91 | 53.1 | M½ | 53 | 13 |
| 7 ◀ | 17.32 | 54.4 | N½ | 54.5 | 14 |
| 7½ | 17.73 | 55.7 | O½ | 55.5 | 15 |
| 8 | 18.13 | 57 | P½ | 57 | 16 |
| 8½ | 18.54 | 58.2 | Q½ | 58 | 18 |
| 9 | 18.95 | 59.5 | R½ | 59.5 | 19 |
| 9½ | 19.35 | 60.8 | S½ | 61 | 20 |
| 10 | 19.76 | 62.1 | T½ | 62 | 21 |
| 10½ | 20.16 | 63.3 | U½ | 63.5 | 22 |
| 11 | 20.57 | 64.6 | V½ | 64.5 | 24 |
| 11½ | 20.98 | 65.9 | W½ | 66 | 25 |
| 12 | 21.38 | 67.2 | X½ | 67 | 26 |
| 12½ | 21.79 | 68.5 | Z | 68.5 | 27 |
| 13 | 22.2 | 69.7 | Z+1 | 69.5 | 29 |
| 13½ | 22.6 | 71 | Z+2 | 71 | 30 |
| 14 | 23.01 | 72.3 | Z+3 | 72.5 | 31 |
| 14½ | 23.42 | 73.6 | Z+4 | 73.5 | 32 |
| 15 | 23.82 | 74.8 | Z+5 | 75 | 33 |
How is a size converted?
Every size is first turned into a circumference: US → π × (11.63 + 0.8128 × size); UK → 37.5 + 1.25 × letter; EU → the size itself; Japan → π × (13 + (size − 1) ÷ 3). Then each scale returns its nearest stocked step to that circumference.
Worked example. UK L is the 12th letter (A = 0, so L = 11): 37.5 + 1.25 × 11 = 51.25 mm around. On the US scale that is a diameter of 16.31 mm and a size of (16.31 − 11.63) ÷ 0.8128 = 5.76: nearest quarter size 5¾, 0 mm above it. EU 51.5; Japan 11.
When the nearest size is not close
UK letters are 1.25 mm apart, US quarter sizes 0.64 mm, so a UK size always lands within half a US quarter step (0.32 mm); the other way round, a US size can fall between two UK halves. The gap in brackets tells you which way to lean. For a ring that will not be resized, lean to the larger size for a wide band and the smaller for a thin one.
Scales this converter leaves out
India and some older European charts use diameter-based numbers, and Switzerland’s old scale was the circumference minus 40. If a chart gives a size in mm, type it on the EU scale if it is a circumference (about 45 to 70) or into the chart page’s finder as a diameter if it is a diameter (about 14 to 23).
Sizes in millimetres
The ring size in mm page lists every size’s diameter and circumference; it is the quickest check when a seller quotes a measurement rather than a size.
Questions about converting sizes
What is a US 7 in UK, EU and Japanese sizes?
US 7 is 54.4 mm around: nearest UK N½, EU 54.5, Japan 14. The converter shows how far each is from exact.
What is a UK L in US sizes?
UK L is 51.25 mm around, which is US 5¾ to the nearest quarter size (5.76 exactly).
Why does the converter show a quarter size?
US rings are made in quarter sizes, so the nearest quarter is the most useful answer. The brackets show the gap: “+0.3 mm” means your size is 0.3 mm of circumference above the one shown. Under about 0.3 mm the converter says “exact”.
Is EU size the same as French or ISO size?
Yes. ISO 8653 defines the size as the inner circumference in millimetres, and the French, German, Swiss and most other European scales now use it. Older Swiss and German scales (diameter-based, or “minus 40”) still appear on some charts.
Are Japanese and Chinese sizes the same?
The same numbered scale is used across much of East Asia, starting at 13 mm inner diameter for size 1 and adding a third of a millimetre per size. Hong Kong jewellers often quote it too.