Ring size chart for US, UK, EU, Japan, China and Russia
A US 7 is a UK N½, an EU/ISO 54.4 and a Japanese 14, which is a ring with a 17.3 mm inner diameter. Every ring size system in the world describes the same two numbers: the ring’s inner diameter and its inner circumference in millimetres. Convert by matching the millimetres, not the labels.
Ring sizes look like six unrelated systems. They are not. Every one of them is a label attached to the same physical fact, the inner diameter of the ring in millimetres. Once you have that number, every other column follows automatically.
The complete international ring size chart
| US / CA | UK / AU | EU / ISO | Japan | China | Russia | Diameter |
|---|---|---|---|---|---|---|
| 3 | F | 44.0 | 4 | 4 | 44.0 | 14.0 |
| 3.5 | G½ | 45.5 | 5 | 5 | 45.5 | 14.5 |
| 4 | H | 46.8 | 7 | 7 | 46.8 | 14.9 |
| 4.5 | I½ | 48.0 | 8 | 8 | 48.0 | 15.3 |
| 5 | J½ | 49.3 | 9 | 9 | 49.3 | 15.7 |
| 5.5 | K½ | 50.6 | 10 | 10 | 50.6 | 16.1 |
| 6 | L½ | 51.9 | 12 | 12 | 51.9 | 16.5 |
| 6.5 | M½ | 53.1 | 13 | 13 | 53.1 | 16.9 |
| 7 | N½ | 54.4 | 14 | 14 | 54.4 | 17.3 |
| 7.5 | O½ | 55.7 | 15 | 15 | 55.7 | 17.7 |
| 8 | P½ | 57.0 | 16 | 16 | 57.0 | 18.1 |
| 8.5 | Q½ | 58.3 | 17 | 17 | 58.3 | 18.6 |
| 9 | R½ | 59.5 | 18 | 18 | 59.5 | 18.9 |
| 9.5 | S½ | 60.8 | 19 | 19 | 60.8 | 19.4 |
| 10 | T½ | 62.1 | 20 | 20 | 62.1 | 19.8 |
| 10.5 | U½ | 63.4 | 22 | 22 | 63.4 | 20.2 |
| 11 | V½ | 64.6 | 23 | 23 | 64.6 | 20.6 |
| 11.5 | W½ | 65.9 | 24 | 24 | 65.9 | 21.0 |
| 12 | Y | 67.2 | 25 | 25 | 67.2 | 21.4 |
| 12.5 | Z | 68.5 | 26 | 26 | 68.5 | 21.8 |
| 13 | Z+1 | 69.7 | 27 | 27 | 69.7 | 22.2 |
How do you read the chart?
Each column is a different naming convention for the same underlying measurement, and knowing what each one is counting makes the whole table easier to trust.
US and Canada use numbers in quarter and half steps. Each full US size is about 0.81 mm of diameter, which is why half sizes exist and quarter sizes are mostly a custom option.
UK, Australia and Ireland use letters in half-letter steps, running from A at the small end through Z and then continuing as Z+1, Z+2 and so on for larger fingers.
EU and ISO is not really a size at all. It is the inner circumference in millimetres, which is why the numbers sit in the forties, fifties and sixties. The standard is ISO 8653.
Japan uses its own integer scale, running roughly from 1 to 27.
China uses the same integer scale as Japan on most conversion charts, including the one built into Ring Sizer.
Russia matches EU and ISO: circumference in millimetres.
What is the maths behind the chart?
If you ever want to check a chart rather than take it on trust, the relationship the industry uses for US sizes is straightforward:
Inner circumference in mm = 36.537 + 2.5535 × US size
Divide that by π to get the diameter. A US 7 gives 36.537 plus 17.875, which is 54.41 mm of circumference, and 54.41 divided by π is 17.3 mm of diameter. That is exactly what the table above says, and exactly what Ring Sizer shows in the app.
Being able to reproduce the numbers matters more than it sounds. Conversion charts on the open web disagree with each other surprisingly often, usually at the extremes of the range where different sources round differently. A chart you can derive is a chart you can check.
Sellers are inconsistent about which they quote and frequently do not say. If a number falls between 14 and 23 it is almost certainly a diameter. Between 44 and 70 it is a circumference. Confusing the two is the single most common ordering mistake in international jewellery.
Convert any size instantly
Which column does your seller mean?
| If the seller is… | They will quote | Watch out for |
|---|---|---|
| A US or Canadian retailer | US numbers such as 6, 6½, 7 | Half sizes exist; quarter sizes usually do not |
| A UK, Irish or Australian jeweller | Letters such as N, N½, O | Some use N where others use N½ |
| A European brand | ISO circumference such as 52, 54, 56 | Usually whole millimetres only |
| A Japanese brand | Integers such as 13, 14, 15 | Not the same as Chinese numbering on every chart |
| An Etsy or independent maker | Anything at all | Always ask for the inner diameter in mm |
When you are not sure, send the millimetre diameter. It is the only unambiguous answer, any jeweller anywhere can work from it, and it removes an entire category of transcription error from the transaction.
How should you handle half sizes and rounding?
US rings are commonly made in half sizes, and each one represents about four tenths of a millimetre of diameter. Quarter sizes exist but they are usually a custom order that costs more and takes longer, which means for most purchases the half size is the real unit of choice.
Your measurement will rarely land exactly on a chart row. When it falls between two sizes:
- Round up on a wide band, on a finger with a large knuckle, or if you tend to run warm.
- Round down on a very thin band, or if you measured in the evening in hot weather and the reading is at the top of its usual range.
- Never round more than a quarter size in either direction without measuring again.
Quoting a result to two decimal places implies a precision that no home method delivers and no high-street jeweller will cut to. The effort is better spent on measuring at the right time of day, which moves the answer considerably more than a decimal place does.
What can a size chart not tell you?
A chart describes a circle. It knows nothing about three things that materially change how a ring fits.
Band width. A 6 mm band feels tighter than a 2 mm band at the same nominal size, because it touches more skin and has further to travel across the knuckle. Add a half size for anything 5 mm or wider. The wide band guide explains why.
Interior profile. A comfort-fit band with a domed interior runs roughly a quarter to a half size large compared with a flat band of the same nominal size, because less of it touches the finger.
Knuckles. If your knuckle is significantly wider than the base of your finger, the chart’s answer will not be the answer, and no amount of precision in the measurement changes that. Read the big knuckle guide before ordering.
What are the average sizes, for a sanity check?
The most commonly ordered women’s sizes cluster between a US 5½ and a US 7. Men’s cluster between a US 9 and a US 11.
That is not a rule and plenty of people sit outside it. It is a way of catching a measurement that has gone badly wrong. If your result lands well outside those bands, check the three usual suspects before ordering: that you measured the inner edge rather than the outer one, that you did not confuse circumference with diameter, and that you measured the finger the ring is actually for.
There is more detail, including where published averages come from and why sources disagree, in the average ring size guide.
Should you print this chart or use it on screen?
Either works, with one condition attached to printing.
A printed chart is only accurate if it prints at exactly one hundred percent scale, and printer drivers routinely apply “fit to page” without saying so. A two percent scale error moves every circle on the page by roughly a full ring size. If you do print it, hold a bank card against a printed reference before trusting anything on the sheet.
Using it on screen avoids that problem entirely, provided the app knows your device’s pixel density rather than assuming one. That distinction is covered in the printable ring sizer guide, which explains what goes wrong with both approaches and how to verify either in about ten seconds.