A ring is sized on the finger it lives on, past the knuckle it has to cross. This chart leads with millimetres because millimetres are the only column every sizing system agrees on.
Checked and updated October 2026
The ruling: measure the finger's circumference in millimetres and let that number rule. It is your EU size outright, and it converts cleanly to US and UK. Skip the string; it stretches and lies by up to a full size. A paper strip, measured three times at the end of the day, lands within half a size. Between sizes, take the larger.
In this guide
The conversion table: US, UK, EU, millimetres
Compiled by our data team from the ISO 8653 sizing standard and the published charts of the major jewellers, cross-checked across four independent references, which agree on every diameter and circumference below. The columns are ordered by honesty: inner circumference is a measurement, EU is that measurement rounded (a 59.5 mm finger is a European 60), US is a scale built on the measurement, and UK letters are the loosest of the four, which is why the note below the table matters.
| US size | Inner diameter (mm) | Inner circumference (mm) | UK size | EU size |
|---|---|---|---|---|
| 5 | 15.7 | 49.3 | J½ | 49 |
| 5.5 | 16.1 | 50.6 | K½ | 51 |
| 6 | 16.5 | 51.9 | L½ | 52 |
| 6.5 | 16.9 | 53.1 | M½ | 53 |
| 7 | 17.3 | 54.4 | N½ | 54 |
| 7.5 | 17.7 | 55.7 | O½ | 56 |
| 8 | 18.1 | 57.0 | P½ | 57 |
| 8.5 | 18.5 | 58.3 | Q½ | 58 |
| 9 | 19.0 | 59.5 | R½ | 60 |
| 9.5 | 19.4 | 60.8 | S½ | 61 |
| 10 | 19.8 | 62.1 | T½ | 62 |
| 10.5 | 20.2 | 63.4 | U½ | 63 |
| 11 | 20.6 | 64.6 | V½ | 65 |
| 11.5 | 21.0 | 65.9 | W½ | 66 |
| 12 | 21.4 | 67.2 | X½ | 67 |
| 12.5 | 21.8 | 68.5 | Y½ | 69 |
| 13 | 22.2 | 69.7 | Z½ | 70 |
The quick answers everyone lands here for: most men wear a US 8 to 12, and the average is a 9 to 10, a circumference of about 59.5 to 62.1 mm. A 60 mm finger is a US 9.5 and a European 60. A US 10 is a UK T½. And the honest footnote this chart prints because others do not: UK letter charts disagree with each other by a half step, so one maker prints R where this chart prints R½ for the same finger. Both are quoting a real chart. The diameter and circumference columns never disagree, which is why they sit in the middle of the table and why every conversion on this page runs through them.
The paper strip method, with its error bars
Five minutes, once, and you can order a ring from any system on earth. You need a strip of paper about 5 mm wide, a fine pen, and a ruler with millimetres.
1. Measure the finger the ring is for, on the hand it will live on; the dominant hand runs about half a size larger. 2. Wrap the strip at the base, snug against the skin, flush but not denting it. Paper, not string: string stretches under its own tension and adds one to two millimetres you do not have. 3. Mark the overlap with the pen where the end meets the strip. 4. Lay it flat and read the millimetres. That is your inner circumference: find it in the table and read across. 5. Do it three times and take the middle reading. Now the error bars, printed because a measurement without them is a rumour: a half size is only about 1.3 mm of circumference, so a 1 mm slip in the wrapping moves you most of a half size. Three careful readings cluster within that, which makes the strip method good to about half a size. If you own a ring that already fits the finger, measure its inside diameter across the widest point instead and read the diameter column: it is the most accurate home method there is, good to about a quarter size.
Knuckle vs base: the gate and the seat
A ring has to satisfy two different measurements on the same finger. The base is where it sits; the knuckle is the gate it crosses twice a day. Measure both with the strip. If your knuckle and base read the same, order that size and stop reading. If the knuckle reads bigger, and on many hands it reads 1 to 2 mm bigger, the knuckle sets the size: order for the knuckle, because a ring that cannot pass it is jewellery for a drawer. A ring sized to a much larger knuckle will spin at the base, and that is a solved problem rather than a wrong size: a jeweller can add sizing beads or a small inner bridge, and a comfort-fit profile, rounded on the inside, passes a knuckle more kindly than a flat one. The verdict our sizing desk gives every reader: fit for the knuckle, furnish for the base. Sizing down to stop the spin just moves the problem to the gate.
Band width and the daily swing
Width. The chart assumes a standard band. A band of 6 mm or wider covers more finger and presses flesh above and below it, so it wears tighter than its size: go half a size up at 6 mm, and treat 8 mm and above as a full fitting conversation. Bands of 2 to 4 mm wear true. The daily swing. Your finger is not one size across a day. It is smallest cold and first thing in the morning, largest warm and in the evening, and the swing runs to about half a size; salt, exercise, heat and flying all push it upward. So the method on this page specifies its conditions: measure in the evening, at room temperature, hands warm and dry, and if the reading lands between sizes on repeated evenings, the larger size is the honest one. A ring fitted to a morning finger is a ring that sticks in August.
The five sizing mistakes
1. Measuring with string. It stretches, reads long, and the ring arrives loose; the error can reach a full size. 2. Measuring a cold morning finger. You have sized for the smallest your finger ever is. 3. Sizing to the base when the knuckle is the gate. The ring fits beautifully in the box and never reaches the finger. 4. Forgetting the band. The chart size in a 7 mm band wears half a size smaller than the same size in a 3 mm band. 5. Converting by letters alone. US to UK by letter charts can land you half a size out before the ring is even made; convert through millimetres and the argument disappears.
The Ruling
Circumference in millimetres is the only number that travels between systems unchanged: it is your EU size, it converts to US and UK without argument, and it fits on a ruler. Paper strip, three readings, evening, warm hands. Fit for the knuckle, furnish for the base, add half a size for a wide band, and take the larger when the readings straddle two sizes. Our full sourcing standard is on the Methodology page.
FAQ
What is the average ring size for men?
US 9 to 10, with most men landing somewhere in the 8 to 12 range. In the measurement this chart leads with, that is an inner circumference of about 59.5 to 62.1 mm. The average is a starting guess only: the same hand carries different sizes on different fingers, and the dominant hand usually runs about half a size larger.
How accurate is the string method for ring size?
String is the least accurate home method, because it stretches as you wrap it and quietly adds one to two millimetres. Since a half size is only about 1.3 mm of circumference, a stretched string can put you a full size too big, and the ring arrives loose. A paper strip does not stretch. Measured three times and read at the middle value, it lands within about half a size.
Should a ring fit tight or loose?
Neither. The test is the knuckle: the ring should need a firm push and a slight twist to pass it, then sit at the base without spinning freely when your hand is cold and relaxed. If it slides over the knuckle with no resistance, it is too big and it will leave the same way. If it will not pass the knuckle at all, no base measurement matters; the knuckle is the gate and it sets the size.
Do wide bands fit differently?
Yes. A band of 6 mm or wider covers more of the finger and grips flesh on both edges, so it wears tighter than a narrow band of the same size. The standard adjustment is half a size up at 6 mm, and it is worth a full conversation with the jeweller at 8 mm and above. Narrow bands of 2 to 4 mm wear true to the chart.
Can your ring size change during the day?
Yes, by up to half a size. Fingers run smallest when cold and first thing in the morning, and largest in warmth and by the end of the day; salt, exercise and a long flight all push them up. That is why the method on this page says measure in the evening, at room temperature, on more than one day if your number falls between sizes.
How do UK ring sizes convert to US sizes?
Convert through millimetres, never letter to number directly, because UK letter charts disagree with each other by a half step: one maker's R is another's R and a half. Measure the finger's inner circumference in millimetres, find it in the chart, and read across. The millimetre column is the one column no two charts argue about.
Next
The wrist next to that hand is ruled by a different pair of numbers in our Watch Case Size Guide, Utility No. 05, where diameter turns out to be the marketing number and lug-to-lug the fit. The neck is covered by the Necklace Length Guide, Utility No. 03. And the family's founding chart still settles more arguments than any of them: the Shoe Size Conversion Chart, Utility No. 01.