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Quickly convert ring sizes across Hong Kong, US, EU, UK, and Japan standards using your finger circumference or diameter, with measurement tips and common mistakes to avoid.
Record the number of millimeters by lapping your fingers around the root with a piece of paper or a soft ruler
Measurement Hints
The strips should be snapped together but not tightened. It is recommended to measure 2 to 3 times at room temperature and when the finger state is natural, and the more stable value should prevail.
19 Japan-code rows from Tiffany Japan. Not HK/CN sizing. Diameters are circumference/pi rounded 0.1mm; fitting needs separate confirmation.
| Tiffany Japan code | Inner circumference (mm) | Inner Diameter (mm) |
|---|---|---|
| 4 | 44.2 | 14.1 |
| 6 | 45.5 | 14.5 |
| 7 | 46.8 | 14.9 |
| 8 | 48.0 | 15.3 |
| 9 | 49.3 | 15.7 |
| 10 | 50.6 | 16.1 |
| 11 | 51.9 | 16.5 |
| 13 | 53.1 | 16.9 |
| 14 | 54.4 | 17.3 |
| 16 | 55.7 | 17.7 |
| 17 | 57.0 | 18.1 |
| 18 | 58.3 | 18.6 |
| 19 | 59.5 | 18.9 |
| 20 | 60.8 | 19.4 |
| 21 | 62.1 | 19.8 |
| 23 | 63.4 | 20.2 |
| 24 | 64.6 | 20.6 |
| 26 | 68.5 | 21.8 |
| 27 | 69.7 | 22.2 |
Comparison table is for code selection reference only
19 Japan-code rows from Tiffany Japan. Not HK/CN sizing. Diameters are circumference/pi rounded 0.1mm; fitting needs separate confirmation.
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
This lookup compares a measurement in millimeters with a fixed set of 19 Japanese ring size codes and returns the closest row. The reference values come from Tiffany’s Japan size guide. It is a brand and market specific reference, not a universal Japanese, US, Hong Kong, China, UK, or EU conversion chart. The available rows run from Japanese code 4 at 44.2 mm circumference to code 27 at 69.7 mm; intermediate codes are not all present.
You can enter either a finger or ring inner circumference, or the inside diameter of a ring that already fits. Circumference is the distance around the inside of the ring or around the finger. Diameter is the straight distance across the inside of a ring, excluding the metal. The chart pairs each listed Japanese code with a circumference and a diameter value. Diameter values are calculated from circumference divided by π and rounded to one decimal millimeter; they are not separate measured manufacturer specifications. For example, the row for code 13 pairs 53.1 mm circumference with a displayed 16.9 mm diameter.
The comparison finds the row with the smallest absolute difference in the selected measurement column. It reports that row’s code, paired circumference and diameter, and the size of the measurement difference. It does not interpolate between rows or guarantee how a particular ring will fit.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
For a finger measurement, wrap a narrow strip of paper or flexible tape around the finger where the ring will sit, mark the overlap, then measure the strip in millimeters. For an existing ring, measure straight across its inside opening at the widest point.
Choose circumference for a wraparound measurement, or diameter for an existing ring’s inside width. Enter the value in millimeters. Do not enter an outside ring measurement or a number in inches.
The result names the nearest Japanese code and shows the reference row’s circumference and calculated diameter. The difference is the distance from your input to the row in the dimension you selected, rounded to 0.1 mm.
If your measurement is below or above the table, the chart still shows the nearest boundary row and marks the input as out of range. Treat that as a boundary reference, not a size recommendation for a measurement the table does not cover.
Repeat a finger measurement to check that the reading is consistent. Keep the paper snug without pulling it tight.
Use cases
See how the tool fits into real work and everyday tasks.
Measure the intended wearing position, enter its circumference in millimeters, and use the nearest Japanese code as a reference to discuss sizing with the seller or compare against the specific ring’s size information.
Measure the inside diameter of that ring and enter it in diameter mode. The closest row shows the paired circumference and code, giving you a compact reference to share when asking about a similar ring.
Q&A
Find concise answers to common questions and confusing cases.
No. It displays only the listed Japanese codes and their paired millimeter measurements. It does not calculate US, EU, UK, Hong Kong, or China size equivalents.
The tool always selects the closest row, so an out-of-range value maps to the nearest endpoint. The out-of-range message means the table does not cover your measurement; it does not extend the listed size range.
No. The diameter shown is calculated from each circumference as circumference ÷ π and rounded to 0.1 mm. Use it as a paired reference value, not as a separately verified physical measurement.
The chart returns whichever row is numerically closer in the dimension you entered; if two rows are equally close, the first row in the chart order is selected. For an actual purchase, check the seller’s guidance for the specific ring and confirm fit when possible.
Notes
Review scope, result limitations, and important precautions before use.
Ring fit depends on the ring and the wearer, and this lookup has no fit test or brand-independent conversion. The reference contains only its listed Japanese codes, so do not interpret a nearest match as proof that a ring from another maker will fit. If the result is near a boundary, out of range, or for a significant purchase, verify sizing with the seller or try the specific ring on.
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