Shopping Guide
HELP / FAQs
By onemall 
TL;DR
Japanese ring sizes are whole numbers called 号, starting at 1号 = 13.00 mm inner diameter and growing by exactly one third of a millimetre per size. To convert to US sizing, the fastest anchors are 9号 = US 5, 13号 = US 6.5, 17号 = US 8.25 and 21号 = US 10. There are no half sizes in Japan.
- 1号 = 13.00 mm diameter / 40.8 mm circumference; every step up adds 1.05 mm of circumference.
- Japanese 号 ≈ (US size × 2.4) + 4 as a rough mental shortcut — use the chart for accuracy.
- 9号 is the most common women’s size in Japan; 17号 is the common men’s size.
- No half sizes. Falling between two 号 means rounding up, not down.
- Match on circumference, not diameter — string-measuring your finger gives circumference directly.
As of September 2026, Japanese jewellery has become one of the harder categories to buy from abroad — not because of stock, but because of sizing. Domestic silver labels, anime and game collaboration rings, and bridal makers all list in 号 only, with no US column anywhere on the page, and rings are the one accessory that cannot be “close enough”. This chart is the whole conversion, plus the two traps that cost people a resize fee.
How the Japanese ring size system works
Japan uses a scale that is refreshingly simple once you see the arithmetic. Size 1号 has an inner diameter of 13.00 mm. Each subsequent size adds exactly ⅓ mm to the diameter, which works out to about 1.05 mm of inner circumference[1]. So 7号 is 15.00 mm across, 13号 is 17.00 mm, and 19号 is 19.00 mm — every sixth size is a clean whole millimetre.
The US scale is built the same way but from different constants: US size 1 has a 39.1 mm inner circumference and each full US size adds about 2.55 mm[1]. Because a US step is roughly 2.4 times a Japanese step, Japanese sizing is finer — which is good news, because it means there is almost always a 号 that lands within half a millimetre of your US size.
Japanese ring size to US conversion chart
Sizes 1号 through 27号 cover essentially every ring sold in Japan. Diameter and circumference are the physical measurements; the US column is the nearest quarter size.
| Japanese size (号) | Inner diameter (mm) | Inner circumference (mm) | US size |
|---|---|---|---|
| 1号 | 13.00 | 40.8 | 1.75 |
| 2号 | 13.33 | 41.9 | 2.0 |
| 3号 | 13.67 | 42.9 | 2.5 |
| 4号 | 14.00 | 44.0 | 3.0 |
| 5号 | 14.33 | 45.0 | 3.25 |
| 6号 | 14.67 | 46.1 | 3.75 |
| 7号 | 15.00 | 47.1 | 4.25 |
| 8号 | 15.33 | 48.2 | 4.5 |
| 9号 | 15.67 | 49.2 | 5.0 |
| 10号 | 16.00 | 50.3 | 5.5 |
| 11号 | 16.33 | 51.3 | 5.75 |
| 12号 | 16.67 | 52.4 | 6.25 |
| 13号 | 17.00 | 53.4 | 6.5 |
| 14号 | 17.33 | 54.5 | 7.0 |
| 15号 | 17.67 | 55.5 | 7.5 |
| 16号 | 18.00 | 56.5 | 7.75 |
| 17号 | 18.33 | 57.6 | 8.25 |
| 18号 | 18.67 | 58.6 | 8.75 |
| 19号 | 19.00 | 59.7 | 9.0 |
| 20号 | 19.33 | 60.7 | 9.5 |
| 21号 | 19.67 | 61.8 | 10.0 |
| 22号 | 20.00 | 62.8 | 10.25 |
| 23号 | 20.33 | 63.9 | 10.75 |
| 24号 | 20.67 | 64.9 | 11.0 |
| 25号 | 21.00 | 66.0 | 11.5 |
| 26号 | 21.33 | 67.0 | 12.0 |
| 27号 | 21.67 | 68.1 | 12.25 |
Larger sizes exist — Japanese charts commonly run to 30号 and some makers go further — and they continue the same ⅓ mm progression.
Quick answers for the most-searched sizes
- Japanese ring size 9 = US 5.0 (49.2 mm inner circumference).
- Japanese ring size 10 = US 5.5 (50.3 mm inner circumference).
- Japanese ring size 11 = US 5.75 (51.3 mm inner circumference).
- Japanese ring size 13 = US 6.5 (53.4 mm inner circumference).
- Japanese ring size 14 = US 7.0 (54.5 mm inner circumference).
- Japanese ring size 15 = US 7.5 (55.5 mm inner circumference).
- Japanese ring size 17 = US 8.25 (57.6 mm inner circumference).
- Japanese ring size 18 = US 8.75 (58.6 mm inner circumference).
- Japanese ring size 19 = US 9.0 (59.7 mm inner circumference).
- Japanese ring size 23 = US 10.75 (63.9 mm inner circumference).
US ring size to Japanese: the reverse chart
Buying from a Japanese site means you must pick a 号. This table takes each US size, gives its true inner circumference, and shows the closest Japanese size and how far off it is:
| US size | Inner circumference (mm) | Nearest Japanese size | Difference |
|---|---|---|---|
| US 4.0 | 46.8 | 7号 | +0.3 mm |
| US 4.5 | 48.0 | 8号 | +0.2 mm |
| US 5.0 | 49.3 | 9号 | -0.1 mm |
| US 5.5 | 50.6 | 10号 | -0.3 mm |
| US 6.0 | 51.9 | 12号 | +0.5 mm |
| US 6.5 | 53.1 | 13号 | +0.3 mm |
| US 7.0 | 54.4 | 14号 | +0.1 mm |
| US 7.5 | 55.7 | 15号 | -0.2 mm |
| US 8.0 | 57.0 | 16号 | -0.5 mm |
| US 8.5 | 58.2 | 18号 | +0.4 mm |
| US 9.0 | 59.5 | 19号 | +0.2 mm |
| US 9.5 | 60.8 | 20号 | -0.1 mm |
| US 10.0 | 62.1 | 21号 | -0.3 mm |
| US 10.5 | 63.3 | 22号 | -0.5 mm |
| US 11.0 | 64.6 | 24号 | +0.3 mm |
| US 11.5 | 65.9 | 25号 | +0.1 mm |
| US 12.0 | 67.2 | 26号 | -0.2 mm |
The difference column is the part that matters. Where it is negative, the Japanese ring is fractionally tighter than your US size; where positive, fractionally looser. Anything inside ±0.5 mm is imperceptible on the finger. Where the gap is larger and you are between sizes, take the bigger 号 — a slightly loose band can be resized down cheaply, while a band that will not pass the knuckle is a return.
Japanese ring size vs US, UK, EU, Hong Kong, China and the Philippines
Once you know the circumference, every other system falls out of it. European sizing is the inner circumference in millimetres. Hong Kong sizing happens to use the same step as Japan, offset by two — HK = 号 + 2. Chinese sizing is quoted as the circumference directly. Only the UK and the American scales need a lookup[2].
| Japan (号) | US / American | UK | EU | Hong Kong | China (circumference) |
|---|---|---|---|---|---|
| 4号 | US 3.0 | F | EU 44 | HK 6 | 44.0 mm |
| 5号 | US 3.25 | F ½ | EU 45 | HK 7 | 45.0 mm |
| 6号 | US 3.75 | G | EU 46 | HK 8 | 46.1 mm |
| 7号 | US 4.25 | G ½ | EU 47 | HK 9 | 47.1 mm |
| 8号 | US 4.5 | H | EU 48 | HK 10 | 48.2 mm |
| 9号 | US 5.0 | H ½ | EU 49 | HK 11 | 49.2 mm |
| 10号 | US 5.5 | I | EU 50 | HK 12 | 50.3 mm |
| 11号 | US 5.75 | I ½ | EU 51 | HK 13 | 51.3 mm |
| 12号 | US 6.25 | J | EU 52 | HK 14 | 52.4 mm |
| 13号 | US 6.5 | J ½ | EU 53 | HK 15 | 53.4 mm |
| 14号 | US 7.0 | K | EU 54 | HK 16 | 54.5 mm |
| 15号 | US 7.5 | K ½ | EU 56 | HK 17 | 55.5 mm |
| 16号 | US 7.75 | L | EU 56 | HK 18 | 56.5 mm |
| 17号 | US 8.25 | L ½ | EU 58 | HK 19 | 57.6 mm |
| 18号 | US 8.75 | M | EU 59 | HK 20 | 58.6 mm |
| 19号 | US 9.0 | M ½ | EU 60 | HK 21 | 59.7 mm |
| 20号 | US 9.5 | N | EU 61 | HK 22 | 60.7 mm |
| 21号 | US 10.0 | N ½ | EU 62 | HK 23 | 61.8 mm |
| 22号 | US 10.25 | O | EU 63 | HK 24 | 62.8 mm |
| 23号 | US 10.75 | O ½ | EU 64 | HK 25 | 63.9 mm |
| 24号 | US 11.0 | P | EU 65 | HK 26 | 64.9 mm |
| 25号 | US 11.5 | P ½ | EU 66 | HK 27 | 66.0 mm |
| 26号 | US 12.0 | Q | EU 67 | HK 28 | 67.0 mm |
| 27号 | US 12.25 | Q ½ | EU 68 | HK 29 | 68.1 mm |
Indian and Philippine charts are usually reprints of one of these systems, The Philippines and the USA share one scale, so Filipino buyers can read the US column directly; a listing marked CN is quoting the Chinese circumference in mm. Indian and Philippine charts are otherwise reprints of one of these systems, so match on the millimetre column rather than on a bare number — that is the only value every country agrees on.
How to measure your ring size at home
- Step 1 — Cut a strip. Use paper about 5 mm wide, or a length of non-stretch string.
- Step 2 — Wrap the finger. Snug, at the base of the finger, and check it will slide over the knuckle.
- Step 3 — Mark and measure. Mark the overlap and measure the length in millimetres. That is your inner circumference.
- Step 4 — Read the chart. Find the closest circumference in the table above; that row is your 号.
- Step 5 — Measure twice, at the right time. Fingers swell in heat and late in the day, and shrink in cold. Measure in the evening at room temperature, and take the larger of two readings.
Wide bands sit tighter than thin ones. For a band over about 6 mm wide, most Japanese jewellers suggest going up one 号[2].
What size do Japanese rings actually come in?
Domestic ready-to-wear jewellery is often stocked in a narrow band: women’s rings cluster around 7号 to 13号 with 9号 as the default, and men’s around 15号 to 21号 with 17号 as the default. Fashion and collaboration rings frequently come in only two or three sizes — commonly listed as something like 11号 and 17号 — so the practical question is not “what is my size” but “does my size exist in this drop”. International brands sold in Japan — Pandora among them — usually print their own home sizing alongside the 号, so check which scale a listing is quoting before you order.
| Typical Japanese stock size | US equivalent | Usually sold as |
|---|---|---|
| 7号 | US 4.25 | Women’s small |
| 9号 | US 5.0 | Women’s standard |
| 11号 | US 5.75 | Women’s large / unisex small |
| 15号 | US 7.5 | Men’s small / unisex |
| 17号 | US 8.25 | Men’s standard |
| 21号 | US 10.0 | Men’s large |
Tokyo makers publish the same equivalences on their own size pages[3], so if a brand you are buying lists a US column, it should agree with the chart above to within a quarter size.
How to buy Japanese rings from Japan
- Step 1 — Get your circumference in mm using the method above, then convert to 号.
- Step 2 — Find the ring. OneMall searches Rakuten, ZOZOTOWN, Mercari, Rakuma, Yahoo Auctions and Amazon Japan at once, which matters for jewellery because limited collaboration rings sell out at retail and reappear only on the second-hand platforms.
- Step 3 — Confirm the 号 on the listing. Second-hand listings state the size stamped inside the band. If a listing gives only a diameter in mm, match it against the chart above rather than guessing.
- Step 4 — Order and pay stage one — item price plus the service fee, from ¥200 per order.
- Step 5 — Add an inspection. For a small, high-value item this is worth it: unboxing photos confirm the stamped size and condition before the parcel leaves Japan.
- Step 6 — Consolidate and ship. The first six orders combine free and storage is free for 90 days; then choose EMS, DHL, ECMS or sea mail[4] and price it with the shipping calculator.
- Step 7 — Check duties. Precious-metal jewellery is frequently dutiable at a different rate from general goods — confirm with your own customs authority before ordering[5].
Buying more than jewellery? Our Japanese clothing size conversion chart and Japanese shoe size to US chart cover the other two scales you will meet.
Our proxy fee comparison and guide to buying from Japan cover the rest of the process.
Frequently Asked Questions
What is Japanese ring size 13 in US?
US 6.5. 13号 has a 17.00 mm inner diameter and a 53.4 mm inner circumference.
What is Japanese ring size 9 in US?
US 5.0. 9号 is the most commonly stocked women’s size in Japan, at 49.2 mm inner circumference.
Does Japan use half ring sizes?
Not officially. You will occasionally see 9.5, 12.5 or 18.5 quoted on second-hand listings and by a few makers; those are maker-specific half steps worth about half a millimetre of circumference. Standard Japanese sizes are whole numbers only. Because a Japanese step is smaller than a US step, this costs less precision than it sounds — but when you sit between two 号, choose the larger.
How do I convert US ring size to Japanese?
Multiply your US size by roughly 2.4 and add 4, then check the reverse chart above. US 6 lands on 12号 and US 8 on 16号.
Are Japanese ring sizes the same as Chinese or Hong Kong sizes?
No. Hong Kong uses its own numeric scale and mainland Chinese sizing follows circumference in millimetres directly. Only match on the millimetre measurement, never on the bare number.
References
- NIWAKA (Kyoto) — official Japanese ring size guide and JCS/US conversion chart. https://us.niwaka.com/pages/japanese-ring-size-guide
- MOKUMEGANEYA — Japanese ring size converter across international systems. https://www.mokumeganeya.com/e/ringsizeconverter/
- PRMAL (Tokyo) — published ring size chart including Japanese, US and EU equivalents. https://www.prmal.com/pages/size-chart
- Japan Post — international mail services, EMS and rate finder. https://www.post.japanpost.jp/service/send/oversea/index_en.html
- Japan Customs — official English guidance on import and export procedures. https://www.customs.go.jp/english/
Last updated: 2026-09-09.