US ring size to UK ring size
Enter a US ring size to get the matching UK letter size used in Britain, Ireland and Australia.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter us 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
Diameter (mm) = 25.4 × (0.458 + 0.032 × US size), circumference = π × diameter. UK letters: A = 37.5 mm, each letter adds 1.25 mm, each half size 0.625 mm.
Example
Inputs: US size = 7. Result: UK size: N½; Inner circumference: 54.4 mm; Inner diameter: 17.32 mm.
Limits and caveats
- Sizes are rounded to the nearest step of each system, and shop mandrels can differ slightly.
- Wide bands (over 6 mm) usually need a slightly larger size.
Questions about this tool
What is US size 7 in UK sizes?
About N½, with an inner circumference of roughly 54.4 mm.
Why does the UK use letters?
British Standard BS 6820 numbers sizes with letters A to Z plus half sizes, then Z+1 and up for larger rings.
Is the Australian size the same as the UK size?
Yes, Australia, New Zealand and Ireland use the same letter scale.