💍 EU / Int'l (circumference mm) to Diameter (mm) Converter
Free online tool to convert EU / Int'l (circumference mm) (EU mm) to Diameter (mm) (mm ∅). Enter a value and get instant, accurate results.
Enter a value above to see the result
EU / Int'l (circumference mm) to Diameter (mm) Conversion Table
| EU / Int'l (circumference mm) (EU mm) | Diameter (mm) (mm ∅) |
|---|---|
| 5 EU mm | 1.5915494 mm ∅ |
| 6 EU mm | 1.9098593 mm ∅ |
| 7 EU mm | 2.2281692 mm ∅ |
| 8 EU mm | 2.5464791 mm ∅ |
| 9 EU mm | 2.864789 mm ∅ |
| 10 EU mm | 3.1830989 mm ∅ |
Conversion Formula
Ring size conversion formulas (approximate): EU (mm circ.) = diameter_mm × π diameter_mm = 11.52 + US × 0.832 (±0.1 mm) JP size ≈ US × 2 − 1 (exact for integer sizes) Common size reference: US 5 = EU 49.3 = JP 9 = 15.7 mm diameter US 6 = EU 51.8 = JP 11 = 16.5 mm diameter US 7 = EU 54.4 = JP 13 = 17.3 mm diameter US 8 = EU 57.0 = JP 15 = 18.2 mm diameter US 9 = EU 59.5 = JP 17 = 18.9 mm diameter US 10 = EU 62.1 = JP 19 = 19.8 mm diameter UK ring sizes use letters (F–Z) — UK A ≈ US 2.5, adding ~0.5 US per letter. UK F = US 3 • UK J = US 5 • UK N = US 7 • UK T = US 10
About EU / Int'l (circumference mm) to Diameter (mm) Conversions
This free EU mm to mm ∅ ring size converter gives you the international equivalent. Enter your ring size below for an instant result — includes US, EU, and Japan sizing.
This conversion uses a non-linear (reciprocal) relationship, so a simple multiplication factor does not apply. The formula section below explains the method, and the reference table shows common converted values.
Below you will find a pre-calculated conversion table, the exact formula used, and answers to common questions about EU / Int'l (circumference mm) to Diameter (mm) conversions. All calculations follow internationally recognized standards.
Note on ring sizes: Conversions use a linear approximation (±0.1 mm). Minor variations exist between jewelers and countries. For important purchases, have your finger professionally sized using physical sizing rings.
Frequently Asked Questions
How do I convert EU / Int'l (circumference mm) to Diameter (mm)?
This conversion is non-linear. Use the calculator above for accurate results, or refer to the formula section on this page.
How many Diameter (mm) are in 1 EU / Int'l (circumference mm)?
The relationship between EU / Int'l (circumference mm) and Diameter (mm) is non-linear. Use the calculator above or the reference table on this page for specific values.
Is EU / Int'l (circumference mm) larger or smaller than Diameter (mm)?
The size relationship between EU / Int'l (circumference mm) and Diameter (mm) depends on the input value because this conversion is non-linear (reciprocal).
When would I use Diameter (mm) instead of EU / Int'l (circumference mm)?
Use mm ∅ sizing when the jeweler or retailer you are purchasing from uses that system. For important purchases, have your finger sized professionally — ring size can vary with temperature and time of day.
Related Ring Size Conversions
Related Guides
Ring Size Conversion Guide
Ring sizes vary completely by country. Learn how US, EU, UK, and Japanese ring sizing systems work, how to convert between them, and what the numbers actually measure.
6 min read
US Ring Sizes vs UK Ring Sizes
US and UK ring sizes use completely different systems — numbers vs letters. Learn how to convert between them using diameter measurements and why the two systems diverged.
5 min read
All conversion results are provided for general informational purposes only. Our formulas use internationally recognized conversion factors; however, rounding may affect precision. Do not rely on these results for professional, medical, legal, or engineering decisions without independent verification. Read our full disclaimer.