Millimetres to EU ring size converter
This is the simplest conversion of all: under ISO 8653 the EU ring size equals the inner circumference in millimetres. If your ring measures 54 mm around the inside, it is an EU 54. Enter a circumference (or a diameter to convert) below.
Quick answer
A mm 54.4 is 54 in EU (about 54.4 mm inner circumference). Use the converter for your exact size, or the chart below for the full range.
Between two sizes? Size up for a comfortable fit, see how to measure accurately.
mm → EU at a glance
- 46.7 mm = 47
- 49.3 mm = 49
- 51.8 mm = 52
- 54.4 mm = 54
- 56.9 mm = 57
- 59.5 mm = 59
- 62.0 mm = 62
- 64.6 mm = 65
mm to EU ring size chart
| mmCircumference | EUEU / ISO | mmDiameter |
|---|---|---|
| 46.7 | 47 | 14.9 |
| 48.0 | 48 | 15.3 |
| 49.3 | 49 | 15.7 |
| 50.5 | 51 | 16.1 |
| 51.8 | 52 | 16.5 |
| 53.1 | 53 | 16.9 |
| 54.4 | 54 | 17.3 |
| 55.6 | 56 | 17.7 |
| 56.9 | 57 | 18.1 |
| 58.2 | 58 | 18.5 |
| 59.5 | 59 | 18.9 |
| 60.7 | 61 | 19.3 |
| 62.0 | 62 | 19.7 |
| 63.3 | 63 | 20.1 |
| 64.6 | 65 | 20.5 |
| 65.8 | 66 | 21.0 |
| 67.1 | 67 | 21.4 |
There is almost nothing to convert
If you have an inner circumference in millimetres, you already have the European size. The two are the same number. A ring measuring 54 mm around the inside is an EU 54, and a finger measuring 52 mm takes an EU 52.
The only step is rounding to the nearest whole millimetre, because European sizes are quoted as whole numbers. A measurement of 54.4 mm is an EU 54.
Only if you measured around, not across
The equivalence holds for circumference alone. A diameter measured straight across the inside of a ring is a completely different number, roughly a third of the circumference, and it has to be multiplied by 3.1416 first.
A 17.2 mm diameter is an EU 54. Entered as a circumference it would come out as an EU 17, a size that does not exist for an adult. The converter above has separate inputs for the two, so the safest approach is to choose the one that matches how you actually measured.
Sizes you will see most often
European sizes for adults mostly run from about 44 to 66. Women’s rings cluster around EU 52 to 53 and men’s around EU 59 to 63, though this varies more between individuals than any average suggests.
Because European sizes step a whole millimetre at a time, they are finer than American sizes, which move in steps of about 2.55 mm. If a ring can be made to a European measurement, you can usually get closer to a true fit than an American size chart would allow.
Common questions
How do I convert a mm ring size to EU?
Enter your mm size in the converter above and read the EU result, or find your row in the chart below. Every value is calculated from the ring’s inner circumference, so it works in both directions.
What is a mm 54.4 in EU?
A mm 54.4 is 54 in EU. That ring has an inner circumference of about 54.4 mm.
Related conversions
Or see the full ring size chart.