* Ring size conversion
UK O½ ring size conversion
UK O½ is an inside diameter of 17.6 mm (circumference 55.3 mm). In other systems that is US 7.5 = UK O½ = EU 55 = Japan 13.
Published July 11, 2026
UK O½ — full conversion
- Inside diameter
- 17.6 mm
- Inside circumference
- 55.3 mm
- Japan
- 13
- US / Canada
- 7.5
- UK / Australia
- O½
- EU (ISO)
- 55
Nearby sizes
- Ø 17.2 mm — US 7 = UK N½ = EU 54 = Japan 12
- Ø 18 mm — US 8 = UK P½ = EU 57 = Japan 14
Buying tips for UK O½
- Wide bands feel tighter — consider going up ~½ US size for bands over 6 mm.
- Printable paper sizers are often ¼–½ size off; prefer a metal gauge at a jeweler.
- Selling the ring for gold? Check 18K ring melt value or the karat × weight calculator.
* Frequently asked
FAQ
- Q. What is UK O½ in other ring size systems?
- A. UK O½ converts to US 7.5 = UK O½ = EU 55 = Japan 13.
- Q. What is the diameter of UK O½?
- A. Inside diameter 17.6 mm; inside circumference 55.3 mm.
- Q. How should I measure my finger?
- A. Measure at the end of the day when fingers are warm. The ring must clear the knuckle; if knuckle and base differ, size for the knuckle and consider a comfort-fit band.
- Q. Can every ring be resized to this size?
- A. Most gold and platinum bands can move 1–2 sizes. Tension settings, eternity bands, and some titanium/tungsten rings cannot. See a jeweler before ordering a resize.
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