Ring Size Converter
Convert ring sizes between US, UK letters, EU (circumference in mm) and JP sizes, or from a measured inner diameter or circumference in millimetres.
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What this tool does
Convert ring sizes between US, UK letters, EU (circumference in mm) and JP sizes, or from a measured inner diameter or circumference in millimetres. Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
How to use the Ring Size Converter
- Enter or select convert from.
- Enter or select value.
- Read the calculated result; change any measurement to compare alternatives.
Formula
Standard jeweller's chart lookup (src/data/sizes.ts): each US size maps to an inner diameter; circumference = pi x diameter; EU size = circumference in mm; UK uses the letter scale; JP uses the Japanese numeric scale.
- from
- Convert from
- value
- Value
Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
Worked example
For ring size converter, the following measurements illustrate the exact method: Convert from: us; Value: 7.
Inputs
- Convert fromUS size
- Value7
Result
- US size7
- UK sizeN
- EU size54
- JP size14
- Inner diameter (mm)17.3
- Circumference (mm)54.4
Ring size chart (standard)
| US | Diameter (mm) | Circumference (mm) | UK | EU | JP |
|---|---|---|---|---|---|
| 4 | 14.9 | 46.8 | H | 47 | 7 |
| 4.5 | 15.3 | 48 | I | 48 | 8 |
| 5 | 15.7 | 49.3 | J | 49 | 9 |
| 5.5 | 16.1 | 50.6 | K | 50.5 | 11 |
| 6 | 16.5 | 51.9 | L | 52 | 12 |
| 6.5 | 16.9 | 53.1 | M | 53 | 13 |
| 7 | 17.3 | 54.4 | N | 54 | 14 |
| 7.5 | 17.7 | 55.7 | O | 55.5 | 16 |
| 8 | 18.1 | 56.9 | P | 57 | 17 |
| 8.5 | 18.5 | 58.2 | Q | 58 | 18 |
| 9 | 18.9 | 59.5 | R | 59.5 | 19 |
| 9.5 | 19.4 | 60.8 | S | 61 | 21 |
| 10 | 19.8 | 62.1 | T | 62 | 22 |
| 10.5 | 20.2 | 63.4 | U | 63.5 | 23 |
| 11 | 20.6 | 64.6 | V | 65 | 24 |
| 11.5 | 21 | 65.9 | W | 66 | 26 |
| 12 | 21.4 | 67.2 | X | 67 | 27 |
| 13 | 22.2 | 69.7 | Z | 70 | 29 |
Results explained
- US size
- US size from the formula above. Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
- UK size
- UK size from the formula above. Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
- EU size
- EU size from the formula above. Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
- JP size
- JP size from the formula above. Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
- Inner diameter (mm)
- Inner diameter (mm) from the formula above. Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
- Circumference (mm)
- Circumference (mm) from the formula above. Chart values are the published standard equivalents; jewellers' mandrels vary slightly by maker. Measure diameter inside the band, or circumference around the finger, in millimetres.
Frequently asked questions
US 7 = 17.3 mm inner diameter, 54.4 mm circumference, UK N, EU 54 and JP 14 on the standard chart.
Measure the inside diameter of the band in millimetres with calipers (or a ruler across the widest inside points), choose 'Inner diameter' and enter it — the converter reads the nearest standard size.
The EU size is simply the finger's circumference in millimetres, so EU 54 means a 54 mm circumference (about 54.4 mm rounds to 54). That makes EU the easiest system to derive from a string measurement.
It should slide over the knuckle with slight resistance and sit snugly without squeezing. Fingers change with temperature and time of day — measure in the evening for the largest realistic size.
Half sizes, wide bands (which feel tighter, often +0.5 size) and maker differences all shift the fit. The chart gives the standard equivalent; for wide bands over 6 mm, many jewellers suggest going up half a size.