Ring size converter
Measure around the finger, or across the inside of a ring that fits. Get the US, UK, EU and Japanese sizes at once.
Wrap a strip of paper around the base of the finger, mark where it overlaps, measure the strip.
- US and Canada
- 7
- UK and Australia
- N 1/2
- EU (ISO 8653)
- 54.5
- Japan
- 14
- Diameter
- 17.3 mm
- Circumference
- 54.4 mm
How the sizes are computed
Every system starts from the inner circumference of the ring. The EU size is that circumference in millimeters (ISO 8653). The US and Canadian size follows C = 2.55 × size + 36.5 mm. UK, Irish and Australian sizes are letters, one letter for every 1.25 mm, with C at 40 mm, and half letters between.
Japanese sizes do not follow a straight line from the circumference; they are fitted on the usual equivalents (US 5 is JP 9, US 7 is JP 14, US 9 is JP 18, US 12 is JP 25).
These are the formulas Find my size uses in Ruban Size when a shopper enters a finger or a ring diameter. They are close to what jewelers use, and a jeweler’s own chart always wins.
Ring size chart, US 3 to 13
| US and Canada | UK and Australia | EU (ISO 8653) | Japan | Inner diameter (mm) | Inner circumference (mm) |
|---|---|---|---|---|---|
| 3 | F 1/2 | 44 | 4 | 14.1 | 44.1 |
| 3.5 | G 1/2 | 45.5 | 6 | 14.5 | 45.4 |
| 4 | H 1/2 | 46.5 | 7 | 14.9 | 46.7 |
| 4.5 | I 1/2 | 48 | 8 | 15.3 | 48.0 |
| 5 | J 1/2 | 49.5 | 9 | 15.7 | 49.3 |
| 5.5 | K 1/2 | 50.5 | 10 | 16.1 | 50.5 |
| 6 | L 1/2 | 52 | 11 | 16.5 | 51.8 |
| 6.5 | M 1/2 | 53 | 12 | 16.9 | 53.1 |
| 7 | N 1/2 | 54.5 | 14 | 17.3 | 54.3 |
| 7.5 | O 1/2 | 55.5 | 15 | 17.7 | 55.6 |
| 8 | P 1/2 | 57 | 16 | 18.1 | 56.9 |
| 8.5 | Q 1/2 | 58 | 17 | 18.5 | 58.2 |
| 9 | R 1/2 | 59.5 | 18 | 18.9 | 59.5 |
| 9.5 | S 1/2 | 60.5 | 19 | 19.3 | 60.7 |
| 10 | T 1/2 | 62 | 20 | 19.7 | 62.0 |
| 10.5 | U 1/2 | 63.5 | 21 | 20.1 | 63.3 |
| 11 | V 1/2 | 64.5 | 23 | 20.5 | 64.5 |
| 11.5 | W 1/2 | 66 | 24 | 21.0 | 65.8 |
| 12 | X 1/2 | 67 | 25 | 21.4 | 67.1 |
| 12.5 | Y 1/2 | 68.5 | 26 | 21.8 | 68.4 |
| 13 | Z 1/2 | 69.5 | 27 | 22.2 | 69.7 |
Approximate equivalents computed from the inner circumference. Diameter and circumference in millimeters.
How to measure
Wrap a paper strip
Around the base of the finger, snug but able to slide over the knuckle.
Mark and measure
Mark where it overlaps, lay it flat and measure in millimeters: that is the circumference.
Or measure a ring
Across the inside of a ring that fits the same finger: that is the inner diameter.
Questions
Should I measure in the morning or the evening?
Fingers swell in the heat. Measure at the end of the day, when they are at their largest, and measure twice.
What if my knuckle is larger than my finger?
The ring has to pass the knuckle. Measure both, and pick a size between the two, closer to the knuckle.
Do wide bands need a different size?
A wide band fits tighter than a thin one of the same size. Between two sizes, take the larger one for a wide band; Find my size does the same.
Is a UK half size the same as a US quarter size?
Not exactly. A UK letter is 1.25 mm of circumference and a US whole size is 2.55 mm, so a UK half letter is close to a US quarter size.
Read more
- How to measureHow to measure your ring size at homeWrap a strip of paper around the base of your finger, mark where it overlaps and measure the length in millimeters: that is your inner circumference, and your EU ring size. No paper? Measure across the inside of a ring that fits the same finger: that is the inner diameter.5 min
- Size conversionRing size conversion chart: US, UK, EU and JapanA US 7 ring measures about 54.4 mm around the inside and 17.3 mm across. That is UK N 1/2, EU 54.5 and Japan 14. The full chart, from US 3 to 13, is below.6 min
Put it on your product pages.
Ruban Size does these conversions inside your size guide, in Find my size, in 22 languages. Free for 5 size charts.