Free tool
Ring size converter
A US size 7 ring measures 17.3 mm across the inside and 54.4 mm around it, which makes it UK N½, EU 54, Japan 14 and India 14. Pick the size system you know, choose your size or type a measurement in millimeters, and the converter shows the same ring in every system.
US size 7
- US / Canada
- 7
- UK / Australia
- N½
- EU / ISO
- 54
- Japan
- 14
- India
- 14
- Inner diameter
- 17.3 mm
- Inner circumference
- 54.4 mm
Which size system your country uses
Choose the option that matches the country where the ring is sold. Country groups are from Wikipedia’s ring size article.
| Country | How sizes work | Choose in the converter |
|---|---|---|
| United States, Canada, Mexico | Numbers, in quarter steps | US / Canada |
| United Kingdom, Ireland, Australia | Letters with half sizes; each letter adds 1.25 mm around | UK / Australia |
| France, Belgium, Austria, the Nordic countries | Inner circumference in mm (ISO 8653) | EU / ISO |
| Germany, the Netherlands, sometimes Russia | Inner diameter in mm | Inner diameter (mm) |
| Italy, Spain, Switzerland | Inner circumference minus 40 mm, so size 10 is 50 mm around | Inner circumference (mm), after adding 40 |
| Japan | Whole numbers | Japan |
| India | Whole numbers | India |
Where the numbers come from
The converter reads the same table as our ring size chart, which covers US 3 to 13 and lists the sources for each column. To measure your finger first, use the printable ring sizer. To see a ring on a hand before you buy or list it, try the virtual ring try-on.
Frequently asked questions
US sizes follow a straight line in millimeters. Your US size is the inner circumference in mm minus 36.5, divided by 2.55, or the inner diameter in mm minus 11.63, divided by 0.8128. A ring 57.0 mm around gives 57.0 minus 36.5, divided by 2.55, which is about 8.0, so US 8. For inches, multiply by 25.4 first: 2.14 inches around is 54.4 mm, a US 7. Or type the mm figure into the converter above.
Each quarter size adds about 0.2 mm of inner diameter and about 0.64 mm of circumference, so US 7.25 is about 17.5 mm across and 55.0 mm around. Choose Inner diameter (mm) and type 17.5: the converter shows the half sizes on either side, US 7 and US 7.5, in every system.
Every system measures the inside of the ring. Each whole US size adds 0.8128 mm of inner diameter. EU sizes follow ISO 8653, which names a ring by its inner circumference in millimeters, so EU 54 is about 54 mm around. UK letters follow BS 6820, where each letter adds 1.25 mm of circumference. Japan and India use whole-number scales that brands print slightly differently, so check a brand's own chart when it has one.
Choose the larger size. A wide band, from about 4 to 6 mm, usually needs a quarter to half size up, and a comfort-fit band can run large. Fingers swell when warm and shrink when cold, so measure later in the day at a normal temperature.
Choose Inner circumference and enter the length, in millimeters, of a paper strip wrapped around the base of your finger. Or choose Inner diameter and enter the width straight across the inside of a ring that fits. Our ring size chart shows three ways to take either measurement at home.
Brands round the same ring differently, by about 0.1 to 0.2 mm, and at US 13 some UK charts say Z+1 where ours says Z½. The Japanese and Indian scales are not linear in millimeters, so those two columns vary most from brand to brand. When a brand publishes its own chart, use that chart for that brand.
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