Ring Size Converter
Ring sizes differ by country: the US uses numbers, the UK and Australia use letters, and Japan uses its own numbering. The one measurement they all share is the inside diameter in millimetres. A US 7 is a UK N½, a Japanese 14, and 17.3 mm across.
- US and Canada7
- UK and AustraliaN½
- Japan and China14
- Inside diameter17.3 mm
- Inside circumference54.3 mm
| US | UK | Japan | Diameter | Circumference |
|---|---|---|---|---|
| 3 | F | 4 | 14.1 mm | 44.3 mm |
| 3.5 | G | 5 | 14.5 mm | 45.6 mm |
| 4 | H | 7 | 14.9 mm | 46.8 mm |
| 4.5 | I | 8 | 15.3 mm | 48.1 mm |
| 5 | J½ | 9 | 15.7 mm | 49.3 mm |
| 5.5 | K½ | 10 | 16.1 mm | 50.6 mm |
| 6 | L½ | 11.5 | 16.5 mm | 51.8 mm |
| 6.5 | M½ | 12.5 | 16.9 mm | 53.1 mm |
| 7 | N½ | 14 | 17.3 mm | 54.3 mm |
| 7.5 | O½ | 15 | 17.7 mm | 55.6 mm |
| 8 | P½ | 16 | 18.1 mm | 56.9 mm |
| 8.5 | Q½ | 17 | 18.5 mm | 58.1 mm |
| 9 | R½ | 18 | 18.9 mm | 59.4 mm |
| 9.5 | S½ | 19 | 19.4 mm | 60.9 mm |
| 10 | T½ | 20 | 19.8 mm | 62.2 mm |
| 10.5 | U½ | 22 | 20.2 mm | 63.5 mm |
| 11 | V½ | 23 | 20.6 mm | 64.7 mm |
| 11.5 | W½ | 24 | 21.0 mm | 66.0 mm |
| 12 | X½ | 25 | 21.4 mm | 67.2 mm |
| 12.5 | Y½ | 26 | 21.8 mm | 68.5 mm |
| 13 | Z½ | 27 | 22.2 mm | 69.7 mm |
How to convert a ring size between countries
Pick the scale you know
Choose whether your size is US, UK, Japanese, a diameter in millimetres, or a circumference.
Enter the size
Type the number or letter. UK letters accept N, N½ or N 1/2, and numbers snap to the nearest real size.
Read every equivalent
All five scales appear at once, including the inside diameter and circumference in millimetres.
Check against the chart
The full chart below highlights your row so you can see the sizes either side of it.
Why use this tool
Five scales at once
US and Canada, UK and Australia, Japan and China, inside diameter, and inside circumference all appear together rather than one pair at a time.
Flexible UK letters
Half sizes can be typed as N½, N 1/2 or just N, and a bare letter finds the nearest half size rather than failing.
Snaps to real sizes
A measured diameter such as 17.1 mm lands on the nearest size that actually exists instead of returning a size no jeweller stocks.
Full chart included
The complete size table is on the page with your size highlighted, so you can see the neighbouring sizes at a glance.
Runs entirely in your browser
Nothing you type is uploaded or stored.
About this tool
Ring sizing has no single international standard. The United States and Canada use numbers that run in half steps, the United Kingdom, Ireland and Australia use letters of the alphabet, Japan and China use their own numeric scale, and much of continental Europe simply quotes the inside circumference in millimetres. A ring bought in one country is routinely mislabelled in another because the scales were never designed to line up.
The one thing every scale agrees on is the physical ring: its inside diameter. That measurement is the anchor here, and every named size maps onto it. A US size 7 is 17.3 millimetres across, which the UK calls N½ and Japan calls 14. Circumference is just the diameter multiplied by pi, which is why European sizes look like 54 or 55 rather than 7 or N.
Because the national scales step in different increments, conversions between them are conventional rather than exact, and different jewellers round slightly differently. If you measure a ring you already own and get a value between two sizes, this tool snaps to the closer one rather than inventing a size that nobody makes. Measure the inside of a ring that fits rather than your finger, and measure at the end of the day when fingers are largest. For other unusual sizing scales there is the shoe size converter and the clothing size converter, and for plain metric work the length converter.
Frequently asked questions
- What is a US size 7 in UK sizing?
- A US 7 is a UK N½, a Japanese 14, and measures 17.3 millimetres inside diameter or about 54.4 millimetres in circumference.
- How do I measure my ring size at home?
- Measure the inside diameter of a ring that already fits, across the widest point, and enter that in millimetres. Measuring a ring is far more reliable than wrapping string around a finger.
- Why do conversion charts disagree with each other?
- Because the national scales step in different increments and never aligned. Where a US half size falls between two UK letters, different jewellers round differently. Any chart is a convention, not a formula.
- What is the difference between diameter and circumference sizing?
- Diameter is the width across the inside of the band, circumference is the distance around it. Circumference is the diameter multiplied by pi, so a 17.3 millimetre diameter is about 54.4 millimetres around.
- Does finger size change?
- Yes. Fingers swell in heat and later in the day, and shrink when cold. Measuring in the evening at normal room temperature gives the most usable size.
- Is my data uploaded anywhere?
- No. The conversion runs in your browser and nothing you type leaves your device.
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