Ring Size Converter: Millimetres to US Ring Size
Ring sizes are just circumferences in disguise. Measure the inside of a ring that fits, in millimetres, and the table gives the matching US size.
What is the Ring Size Converter?
Enter the inner circumference of a ring in millimetres, and the tool finds the nearest standard US ring size from a reference table. Ring sizes vary slightly by country and by ring width, so treat the result as a guide and confirm with a jeweller for an expensive ring.
How to use it
- Enter the inner circumference in millimetres.
- Click Convert Ring Size.
- Read the nearest US ring size.
Worked example
An inner circumference of 54 millimetres is nearest to the table value 54.4 millimetres, which is US size 7.
How do I measure a ring's circumference?
Wrap a thin strip of paper around the inside of a ring that fits, mark it, and measure the strip in millimetres — or measure the inside diameter and multiply by 3.14.
Frequently asked questions
Why is the result approximate?
Because the tool picks the nearest table value, and wide bands and different countries size slightly differently.
Should fingers be measured warm or cold?
Warm, at the end of the day, when fingers are at their largest — a ring that fits cold fingers can feel tight later.