Use it to convert a size you already know, to read a measurement you took at home, or to open one size's own page for the numbers around it. If you need the size of someone who must not find out, the sizing guide covers that part.
Ring size chart
Ring size conversion chart: US, UK, EU and Japan
Every system below describes the same physical thing: the inside circumference of the ring. Find the measurement you have, read across the row, and give the jeweler the millimeter figure alongside the local size so nothing is lost in conversion.
| US / Canada | UK / Australia | EU / ISO (circumference, mm) | Japan / Korea | Inside diameter (mm) |
|---|---|---|---|---|
| 3 | F½ | 44.2 | 4 | 14.1 |
| 3.5 | G½ | 45.5 | 5 | 14.5 |
| 4 | H½ | 46.8 | 7 | 14.9 |
| 4.5 | I½ | 48.0 | 8 | 15.3 |
| 5 | J½ | 49.3 | 9 | 15.7 |
| 5.5 | K½ | 50.6 | 10 | 16.1 |
| 6 | L½ | 51.9 | 12 | 16.5 |
| 6.5 | M½ | 53.1 | 13 | 16.9 |
| 7 | N½ | 54.4 | 14 | 17.3 |
| 7.5 | O½ | 55.7 | 15 | 17.7 |
| 8 | P½ | 57.0 | 16 | 18.1 |
| 8.5 | Q½ | 58.3 | 18 | 18.5 |
| 9 | R½ | 59.5 | 19 | 19.0 |
| 9.5 | S½ | 60.8 | 20 | 19.4 |
| 10 | T½ | 62.1 | 21 | 19.8 |
| 10.5 | U½ | 63.3 | 22 | 20.2 |
| 11 | V½ | 64.6 | 24 | 20.6 |
| 11.5 | W½ | 65.9 | 25 | 21.0 |
| 12 | X½ | 67.2 | 26 | 21.4 |
| 12.5 | Y½ | 68.5 | 27 | 21.8 |
| 13 | Z½ | 69.7 | 29 | 22.2 |
US jewelers quote numeric sizes with half and quarter steps; the EU/ISO number is simply the circumference in millimeters, which is why it converts so cleanly.
Convert a measurement to a ring size
Measure a ring that already fits the right finger, or the finger itself, and enter the number in millimeters.
How to measure at home
- Use a ring they already wear on the target finger. Measure its inside diameter edge to edge with a ruler, or trace the inside edge on paper and measure that circle.
- If you only have the finger, wrap a thin strip of paper snugly around its base at the end of the day, mark where it overlaps, and measure that length in millimeters: that is the circumference.
- Check the knuckle. If it is noticeably larger than the base of the finger, a jeweler can suggest a compromise size, and a plastic sizer set beats string or paper for accuracy.
Conversions are rounded to the nearest standard size, and published charts differ from each other by up to half a size. Treat the result as a close estimate, confirm it with a jeweler's sizer before buying, and check the resizing policy.
How the sizing systems relate
US and Canada
Numbers from about 3 to 13 with half and quarter steps. Each full size adds 0.8128 mm (1/32 inch) of inside diameter, so one US size is roughly 2.5 mm of circumference.
UK, Australia and Ireland
Letters from A upward with half sizes. Each letter is 1.25 mm of circumference, which is why a UK half letter is a finer step than a US half size.
EU and ISO 8653
The inside circumference in millimeters, so 52 means 52 mm around. France, Germany, Spain, Italy and most of continental Europe quote this number, and it converts to any other system without a table.
Japan and Korea
Numbers starting at 1 for a 13 mm inside diameter, each step adding a third of a millimeter. The ladder is finer than US half sizes, so two neighbouring Japanese numbers can map to the same US size.
Brazil, Türkiye, Vietnam, India and neighbours
The circumference minus 40: a 54 mm ring is a 14. Shops keep their own charts, so quote the millimeters alongside the number.
Every US size on its own page
Each page lists one size in every system, the half sizes either side, how common it is and what to do when a measurement falls between sizes.
Quick answers
Frequently asked questions
How do I find my ring size at home?
Measure the inside diameter of a ring that already fits the right finger, or wrap a thin strip of paper around the base of the finger at the end of the day and measure the overlap in millimeters. Enter either number in the converter above to read the closest standard sizes.
What is the most common ring size?
In the US, most women's engagement rings sell between sizes 4.5 and 7.5, with 6 to 6.5 the most frequently quoted average, and most men's bands between 8 and 12. Stock sizes follow those ranges; sizes outside them are usually made to order.
Are UK, EU and US ring sizes the same?
No, but they describe the same circumference. US sizes are numbers, UK sizes are letters, EU/ISO sizes are the circumference in millimeters, and Japanese sizes are numbers on a finer ladder. Read across one row of the chart to move between them.
Should I size up or down between sizes?
Up. A ring can be made smaller more easily than larger, a wide band needs a little more room, and fingers swell in heat and in the evening. Confirm with a jeweler's sizer set before buying, and check the resizing policy.
Need their size without asking?
The sizing guide covers borrowing a ring they already wear, the tells that give a surprise away, and how to plan resizing after the proposal.