💍 US / Canada Ring Size to EU / Int'l (circumference mm) Converter
Free online tool to convert US / Canada Ring Size (US) to EU / Int'l (circumference mm) (EU mm). Enter a value and get instant, accurate results.
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US / Canada Ring Size to EU / Int'l (circumference mm) Conversion Table
| US / Canada Ring Size (US) | EU / Int'l (circumference mm) (EU mm) |
|---|---|
| 5 US | 49.260173 EU mm |
| 6 US | 51.873978 EU mm |
| 7 US | 54.487783 EU mm |
| 8 US | 57.101588 EU mm |
| 9 US | 59.715393 EU mm |
| 10 US | 62.329198 EU 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 US / Canada Ring Size to EU / Int'l (circumference mm) Conversions
The US to EU mm ring size converter handles the differences between international sizing systems. Enter a size below for an instant result.
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.
This page includes a reference table of common US / Canada Ring Size values pre-converted to EU / Int'l (circumference mm), the conversion formula, and frequently asked questions. All values use internationally recognized conversion 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 does the EU ring size system work?
EU (ISO) ring sizes are simply the inner circumference in millimeters — a size 54 ring has a 54 mm inner circumference. That makes the system linear and decimal-friendly: no letters, no half sizes, just the measurement itself.
What is US ring size 9 in EU?
US 9 converts to approximately EU 59.5 — most sellers would fit you with a 59 or 60. The math: US 9 is a 19.0 mm inner diameter, and 19.0 × π ≈ 59.7 mm circumference.
Do EU ring sizes have half sizes?
Not as named sizes — because EU sizes are just millimeters of circumference, the next step up from 54 is 55, which is already finer-grained than a US half size (about 1.3 mm of circumference). Many European jewelers stock every integer size for this reason.
If I'm between EU sizes, should I round up or down?
Round up. A ring a half millimeter loose spins slightly; a ring a half millimeter tight pinches and is hard to remove when fingers swell in heat. Rounding up also leaves room for the knuckle, which is usually wider than the base of the finger.
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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.