Ring size converter
Your ring size, in every country.
Convert instantly between US, UK, EU, Japan and millimetres, or measure your finger at home. Accurate to the ISO 8653 standard, mobile-friendly, and free.
Trusted method · No sign-up · Works on any phone
Three ways to find your size
Convert a size you know
Already have a size in one country? Translate it to any other in a tap.
Use the converter →Measure a ring you own
Calibrate your screen with a bank card and lay a ring on the display.
Open the sizer →Measure your finger
Use string or a strip of paper and our step-by-step guide with a chart.
Read the guide →Ring size chart (US, UK, EU, Japan & mm)
The most common sizes at a glance. Every value is calculated from inner circumference, so the rows line up exactly. Need smaller or larger sizes? See the full ring size chart.
| USUS / Canada | UKUK / AU | EUEU / ISO | JPJapan | mmCircumference | mmDiameter |
|---|---|---|---|---|---|
| 4 | H½ | 47 | 7 | 46.7 | 14.9 |
| 4½ | I½ | 48 | 8 | 48.0 | 15.3 |
| 5 | J½ | 49 | 9 | 49.3 | 15.7 |
| 5½ | K½ | 51 | 10 | 50.5 | 16.1 |
| 6 | L½ | 52 | 11 | 51.8 | 16.5 |
| 6½ | M½ | 53 | 13 | 53.1 | 16.9 |
| 7 | N½ | 54 | 14 | 54.4 | 17.3 |
| 7½ | O½ | 56 | 15 | 55.6 | 17.7 |
| 8 | P½ | 57 | 16 | 56.9 | 18.1 |
| 8½ | Q½ | 58 | 18 | 58.2 | 18.5 |
| 9 | R½ | 59 | 19 | 59.5 | 18.9 |
| 9½ | S½ | 61 | 20 | 60.7 | 19.3 |
| 10 | T½ | 62 | 21 | 62.0 | 19.7 |
| 10½ | U½ | 63 | 22 | 63.3 | 20.1 |
| 11 | V½ | 65 | 24 | 64.6 | 20.5 |
| 11½ | W½ | 66 | 25 | 65.8 | 21.0 |
| 12 | X½ | 67 | 26 | 67.1 | 21.4 |
Popular conversions
Frequently asked questions
How do I convert my ring size to another country?
Pick the system you already know (US, UK, EU, Japan or millimetres) in the converter above, type your size, and every other country’s equivalent appears instantly. All values are calculated from the ring’s inner circumference, so the conversions stay consistent in both directions.
What is the most accurate way to measure ring size at home?
The most reliable home method is to measure the inner diameter of a ring that already fits, in millimetres or inches, and convert it. Our on-screen sizer lets you calibrate the screen with a bank card and lay a ring on the display to read the size. For a wedding or engagement ring, confirm with a jeweller.
Is a US ring size the same as a UK ring size?
No. The US uses numbers (with half sizes) and the UK, Ireland, Australia and New Zealand use letters A to Z. For example, a US 7 is a UK N½. Use the converter to translate between them precisely.
What does the EU / ISO ring size number mean?
Under the ISO 8653 standard, the European ring size is simply the inner circumference of the ring in millimetres. So an EU 54 ring measures 54 mm around the inside, which makes it a useful universal reference.
Why do some ring size charts disagree?
Many older charts round differently or are misaligned by a size, and a few well-known ones are visibly off by about a millimetre. We calculate every value from the official ISO 8653 circumference formula and the Japanese JIS standard, then cross-check against known jeweller measurements.