This ring-size converter translates an inside diameter or circumference into six international ring-size systems.
Everyday life
cm to Ring Size Converter
Convert ring diameter or circumference and look up six international size systems.
Calculator
About this calculator
Formula notes
circumference = diameter x pi; the closest matching row in the captured international size table becomes the reported size.
Worked examples
- Example: a 1.735 cm inside diameter maps to US size 7, UK size O, and France size 55 1/4.
- An inside diameter of 17.35 mm maps to US size 7, UK size O, and France size 55 1/4.
How to use it
- Choose whether you measured inside diameter or circumference.
- Enter the measurement with its unit.
- Read US, UK, France, Germany, Switzerland, and Japan sizes.
Frequently asked questions
Should I measure the ring or the finger?
Measure the inside of a well-fitting ring or use a proper ring gauge; diameter and circumference give equivalent size lookups.
What if the measurement is outside the table?
Sizes are returned only when the measurement matches the captured range; outside values show no size result.
Limits and interpretation
- Ring sizes vary by jeweler, country, and sizing convention; treat the lookup as a reference rather than a guarantee.
- Measurements are sensitive to temperature, fit preference, and how tightly the ring is worn.