UK ring size to US ring size
Pick the UK letter to find the matching US size before buying from a US store.
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How to use it
- Enter uk size.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Letter circumference = 37.5 + 1.25 × letter index (A = 0), plus 0.625 for a half size. US size = (C ÷ (π × 25.4) − 0.458) ÷ 0.032, rounded to the nearest quarter.
Example
Inputs: UK size = N. Result: US size: 6.75; Exact US size: 6.74; Inner circumference: 53.75 mm.
Limits and caveats
- Sizes are rounded to the nearest step of each system, and shop mandrels can differ slightly.
- US sizes usually stop near 15, so larger letters may show as outside the chart.
Questions about this tool
What is UK N in US sizes?
N has a 53.75 mm circumference, which is about US 6.75.
How far apart are two letters?
Each letter adds 1.25 mm of circumference, roughly half a US size.
What does Z+1 mean?
It is the next size after Z, 1.25 mm larger in circumference, used for big rings.