Ring Size Converter
Enter a US ring size to convert it to UK sizing and internal diameter in millimeters, using standard published ring size charts.
How the Ring Size Converter formula works
Ring sizing, like clothing and shoe sizing, follows standardized reference charts rather than a mathematical formula, based on a ring's internal diameter.
Step-by-step calculation
- Look up the entered US ring size in a standard reference chart.
- Read across to find the corresponding UK size and internal diameter in millimeters.
Worked example
A US size 7 ring converts to approximately UK size N and an internal diameter of about 17.3 mm under standard sizing charts.
Frequently asked questions
How can I measure my ring size at home?
Wrap a strip of paper or string around your finger, mark where it overlaps, measure that length, and divide by π (about 3.14159) to estimate the internal diameter — then compare against a size chart. Getting professionally sized at a jeweler is more reliable.
Does ring width affect the size needed?
Yes — wider bands typically fit more snugly than thinner bands at the same labeled size, so many jewelers recommend sizing up slightly for wide rings.