Ring size converter
Convert a ring size between circumference, diameter, European size (as used in France), US and UK sizes — handy for ordering a ring from an overseas site. Fully local calculation, in your browser.
How it works
In France, a ring's size corresponds directly to its inner circumference in millimeters, whereas the United States and the United Kingdom use their own scales (a number for US sizes, a letter for UK sizes). This tool converts across all three systems from a single measurement of your choice.
How do I measure my ring size at home?
Wrap a piece of string or a thin strip of paper around the base of your finger, mark the point where the two ends meet, then measure that length with a ruler: that is your circumference in millimeters. You can also measure the inner diameter of a ring that already fits you well, using calipers or a ruler placed across the opening.
Why does my ring size vary depending on the time of day?
Finger size can vary slightly with temperature, water retention or recent physical activity — fingers tend to swell at the end of the day or in hot weather. It is best to measure your ring size in the evening, at normal room temperature, for a result that represents your average.
Your measurements are neither stored nor transmitted: the calculation stays entirely on your device.