EU ring size 66 in US, UK & Japan

EU/ISO ring size 66 is an inner circumference of about 66 mm (65.9 mm exactly) — that equals US 11.5, UK W½ and Japan 24, with an inner diameter of 20.98 mm.

Illustrative — screen scale varies. Use the true-scale ring below for a real measurement.

EU / ISO: 66
US / Canada: 11.5
UK / AU: W½
Japan: 24
CH / IT / ES: 26
Diameter: 20.98 mm
Circumference: 65.9 mm

Why EU 66 looks larger than US 11.5

Under ISO 8653, the EU (and ISO) ring size number is the ring's inner circumference in millimetres. So EU 66 means the band measures about 66 mm all the way around — a circumference, not a diameter. That's why EU numbers are so much larger than US numbers for the same finger, and why an EU size can be read straight off a millimetre measurement.

50 mm reference bar

True-to-scale ring Printed at 100%, the inside of this ring is 20.98 mm across.

Convert the other way with the EU to US ring size chart, open the US size 11.5 page, see the full chart, or use the converter.

Frequently asked questions

Why does EU 66 use a circumference number?

EU/ISO 66 follows the published circumference convention: about 66 mm around the inside (65.9 mm in this chart), corresponding to a 20.98 mm inner diameter.

How should I confirm EU 66 before ordering?

Check the retailer's own chart and confirm the 20.98 mm inner diameter with a physical sizer or a ring that already fits. Converted labels are a starting point, not a fit guarantee.