Practical measurement and conversion reference
Ring sizing uses completely different systems across countries, a US size 7 is a UK N, an EU 54, and a Japanese size 14. Getting the wrong size online means an expensive return. Measure your finger accurately before ordering.
Standard reference
US / UK / EU with measurements
| US | UK | EU | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|
| 4 | H | 47 | 14.9 | 46.8 |
| 4.5 | I | 48 | 15.3 | 48.0 |
| 5 | J | 49 | 15.7 | 49.3 |
| 5.5 | K | 50 | 16.1 | 50.6 |
| 6 | L | 51 | 16.5 | 51.9 |
| 6.5 | M | 52 | 16.9 | 53.1 |
| 7 | N | 54 | 17.3 | 54.4 |
| 7.5 | O | 55 | 17.7 | 55.7 |
| 8 | P | 56 | 18.1 | 57.0 |
| 8.5 | Q | 58 | 18.5 | 58.3 |
| 9 | R | 59 | 18.9 | 59.5 |
| 10 | T | 62 | 19.8 | 62.1 |
Use this as a standard reference. Jewelry brands may use slightly different sizing tolerances.
Decision workflow
Start with a measurement, not the size printed in an older item. The steps below turn a chart row into a checkable purchase decision.
Measure the finger at the time of day you normally wear rings, then record either inside diameter or circumference in millimetres.
Use one measurement system consistently. Diameter and circumference describe the same ring size, but mixing them produces a false match.
Check the band width and the knuckle. A wide band or a pronounced knuckle can change the practical choice even when the number is correct.
Follow these steps before buying online to get the most accurate size. Measure twice, order once.
The most accurate method is to measure the internal diameter of a ring that already fits you well. Use a ruler and measure across the inside in millimeters.
Alternatively, wrap a thin strip of paper or string around your finger, mark where it overlaps, and measure the length. This is your circumference in mm.
Measure in the evening or after light activity, as fingers swell slightly with warmth. Avoid measuring when cold.
If you are between sizes, go larger for rings with stones and smaller for plain bands.
For rings wider than 6mm, size up by half a size, wider bands fit more snugly against the finger.
Measurements vary by brand. Always check the brand's specific size chart before purchasing — or use the free generator below to build a custom chart for your store.
A ring size is a label for the ring’s inside circumference, the distance around the inside of the band, rather than for a finger. Two national systems can use the same number for different circumferences, and even within one system the same label hides small steps. In the US scale, for example, a size 7 ring measures about 54.4 mm around the inside, which works out to roughly 17.3 mm across the inside diameter; in Japan, a size 7 describes a much smaller ring. The number only becomes useful once you know which scale the seller is using. That is why the safest habit is to work in millimetres: the inside circumference, or the inside diameter, is the physical fact that every national scale translates from. Measure it once, record it, and then read any chart (US, UK, EU, Japanese, or Swiss) against that single value.
You can arrive at your size from either direction. The most dependable home method is to take a ring that already fits the intended finger well and measure its inside diameter across the widest point with a ruler that reads millimetres. The diameter is easier to measure accurately than the circumference, and the chart converts it for you: a 17.3 mm inside diameter is a US 7, and a millimetre or so of difference generally moves you a full size.
If you have no fitting ring, wrap a thin strip of paper around the base of the finger (dental floss works too, and stretches less than string), mark where the end overlaps, and measure that length flat in millimetres. This is your circumference reading. Divide it by 3.14 and you get the diameter, which lets you cross-check one method against the other. Always measure the specific finger the ring is for: the index, middle, and ring fingers differ, and the dominant hand’s fingers usually run about half a size larger.
Two forces pull a ring in opposite directions. The band must pass over the knuckle, which is wider than the base of the finger, but it must then sit securely at the base without sliding off. When the knuckle is noticeably larger than the finger base, which is common, you fit the knuckle and accept that the band may turn at the base, or choose a style that helps, such as an adjustable shank; a jeweller can advise.
A ring that scrapes over the knuckle with real resistance is too small, even if it feels fine once it is on.
Band width changes the fit at the same numerical size. A wide band (roughly 6 mm and above) contacts more skin and feels tighter, so most jewellers suggest going up about half a size for wide styles. Temperature and time of day matter too: fingers are slimmest when cold and first thing in the morning, and swell with heat, exercise, and sometimes salt. Measure when your hands are warm and at a normal time of day, and if the reading sits between sizes, remember that the ring still has to clear the knuckle.
Once you have the circumference in millimetres, the international scales fall into place. The ISO 8653 standard behind European sizing is the simplest: the EU size is the inside circumference in millimetres, rounded, so 54.4 mm is an EU 54, and a US 7 is therefore an EU 54. The UK system uses letters from A to Z, with each step worth about 1.25 mm of circumference and half-sizes between letters; a US 7 corresponds to roughly a UK N or N½. Japanese sizing is numeric again but on its own scale, with a US 7 matching a Japanese 14, and French, German, and Swiss systems each carry their own numbers or letters.
Rather than memorising these pairs, keep the millimetre value. Every reputable chart carries a circumference or diameter column, and matching those columns across two charts is always safer than converting a size label through a third system.
If your measurement falls between two printed sizes, lean larger for a ring with stones or a wide band, and consider the smaller only for a slim plain band, since the material and setting take up room. Ordering larger is also the safer error in general: most plain metal rings can be reduced or enlarged by one to two sizes by a jeweller, and it is easier to make a ring smaller than larger.
Resizing is not a universal safety net. Eternity bands with stones set all the way around, heavily engraved rings, and rings made from very hard metals such as tungsten or titanium usually cannot be resized at all. If the ring is a surprise or a final sale, verify the size twice and check the seller’s exchange policy before committing.
Ring size scales and band measurements vary by brand, so confirm the seller’s chart for the exact ring before buying.
Building a chart for your own store? Create a reusable chart with the free generator.
Common questions about ring size chart answered by our sizing experts.
US ring size 7 equals UK size N½, EU/ISO size 54.4, French size 54, German size 17, Japanese size 14, and Swiss size 14¼. The EU/ISO system uses circumference in mm, the UK uses letters (A–Z), and the US uses numbers 1–13. Use the circumference column for the most universal comparison.
Wrap a thin strip of paper around the base of your finger. Mark where the end meets the strip and measure that length in millimeters. This is your finger circumference. Find that number in the circumference column of the ring size chart to identify your size. Alternatively, measure the diameter of a ring that fits well and look up that value in the diameter column.
Yes. Your ring finger is a different size than your middle or index finger, and your dominant hand's fingers are usually slightly larger. Always measure the specific finger the ring will be worn on, don't assume one size fits all fingers.
Most plain metal rings can be resized 1–2 sizes up or down by a jeweler. However, rings with stones set all the way around (eternity bands), rings made from titanium or tungsten, and heavily engraved rings are very difficult or impossible to resize. When in doubt, order the larger size. It is easier to make a ring smaller than larger.
Japanese ring sizes use a numeric scale based on circumference in mm divided by π (approximately). Japanese size 7 ≈ US 4, Japanese 11 ≈ US 5.5, Japanese 14 ≈ US 7, Japanese 17 ≈ US 8.5, Japanese 20 ≈ US 10. When shopping from Japanese brands like Mikimoto or Tasaki, use the circumference measurement to convert accurately.
