How to use this tool
Choose inside diameter, circumference or a supported US/Canada ring size.
Use millimeters for geometric measurements. Compare the approximate result with a jeweler's sizing before buying.
Circumference = π × inside diameter; choose the nearest supported full US size
Worked example
7 · nearest full US / Canada size
Fixed example using the settings below. Monetary examples use USD; dates and times use their stated reference values. This example stays unchanged when you edit your calculation.
Example inputs
- Input measure: Inside diameter (mm)
- Measurement or size: 17.3
Method illustration: An inside diameter of about 17.3 mm is approximately US size 7.
Assumptions and limits
- Supports only the named full US/Canada sizes, not all regional sizing systems. Circumference in mm is a geometric measurement, not a claim of exact fit.
- Sizing charts and ring widths vary. Measure with a jeweler before buying; values outside the chart are rejected.
Method reference: GIA ring sizing chart
Check or report a result
Check the units, selected calculation and assumptions first. Compare the fixed example above with your inputs to identify what changed.
Report a calculation issue with the page address, hypothetical inputs, result displayed and result expected. Do not include passwords, bank details or other private information.