Ring size from finger circumference
A home method to find your ring size with a string and a ruler, no jeweller needed.
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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 string length around finger and unit.
- 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
The circumference in mm is the EU size. Diameter = circumference ÷ π, US = (C ÷ (π × 25.4) − 0.458) ÷ 0.032.
Example
Inputs: String length around finger = 54, Unit = millimeters. Result: US size: 6.75; UK size: N; EU size (ISO): 54.
Limits and caveats
- String can stretch or wrap at an angle, so measure twice, ideally late in the day when fingers are larger.
- Make sure the ring will pass over the knuckle; you may need a size up.
Questions about this tool
How do I measure my finger?
Wrap a non-stretch string around the base of the finger, mark where it meets, then measure with a ruler.
My finger is 54 mm around. What size?
EU 54, about US 6.75 and UK N.
When should I size up?
When your knuckle is wider than the finger base or the band is wide.