Japan to US ring size converter
Japanese (JIS) sizes are numeric but based on the inner diameter in millimetres, so they climb faster than US numbers. A Japan 12 is about a US 6 and a Japan 14 is about a US 7. China and South Korea commonly use the same scale. Enter a Japan size below.
Quick answer
A Japan 14 is 7 in US (about 54.4 mm inner circumference). Use the converter for your exact size, or the chart below for the full range.
Between two sizes? Size up for a comfortable fit, see how to measure accurately.
Japan → US at a glance
- 7 = 4
- 9 = 5
- 11 = 6
- 14 = 7
- 16 = 8
- 19 = 9
- 21 = 10
- 24 = 11
Japan to US ring size chart
| JPJapan | USUS / Canada | mmCircumference | mmDiameter |
|---|---|---|---|
| 7 | 4 | 46.7 | 14.9 |
| 8 | 4½ | 48.0 | 15.3 |
| 9 | 5 | 49.3 | 15.7 |
| 10 | 5½ | 50.5 | 16.1 |
| 11 | 6 | 51.8 | 16.5 |
| 13 | 6½ | 53.1 | 16.9 |
| 14 | 7 | 54.4 | 17.3 |
| 15 | 7½ | 55.6 | 17.7 |
| 16 | 8 | 56.9 | 18.1 |
| 18 | 8½ | 58.2 | 18.5 |
| 19 | 9 | 59.5 | 18.9 |
| 20 | 9½ | 60.7 | 19.3 |
| 21 | 10 | 62.0 | 19.7 |
| 22 | 10½ | 63.3 | 20.1 |
| 24 | 11 | 64.6 | 20.5 |
| 25 | 11½ | 65.8 | 21.0 |
| 26 | 12 | 67.1 | 21.4 |
What your Japanese size number means
A Japanese size is built from the inner diameter of the ring. Size 1 corresponds to a 13 mm diameter, and every number after it adds about a third of a millimetre. Size 13 is therefore about 17 mm across the inside.
You can work it out without a chart if you need to: add 38 to your Japanese size, then divide by three, and the answer is the inner diameter in millimetres. A Japan 14 gives 52 divided by 3, which is about 17.3 mm.
Converting to the American scale
US sizes are defined by circumference rather than diameter, so the conversion runs through one extra step: diameter to circumference, then circumference to a US number. Multiplying the diameter by 3.1416 does the first part.
Because Japanese sizing is the finer of the two scales, some Japanese sizes share a single US size. A Japan 11 and a Japan 12 both round to a US 6. The 11 sits a little under that size and the 12 a little over, so the 12 is the safer of the two to order. Converting the other way loses that distinction, which is worth knowing if you are buying a ring you cannot return.
Buying in the United States with a Japanese size
American jewellers work in whole and half sizes and will not recognise a Japanese number, so convert before you walk in. Take the millimetre measurement with you as well, since that is the value any jeweller can verify on a mandrel.
If your Japanese size converts to something between two US sizes, size up rather than down, particularly for a wide band. Comfort fit bands are the exception, as their rounded inner edge slides on more easily and tends to run large.
Common questions
How do I convert a Japan ring size to US?
Enter your Japan size in the converter above and read the US result, or find your row in the chart below. Every value is calculated from the ring’s inner circumference, so it works in both directions.
What is a Japan 14 in US?
A Japan 14 is 7 in US. That ring has an inner circumference of about 54.4 mm.
Related conversions
Or see the full ring size chart.