Inches to Ring Size Converter

How to measure your ring size in inches

The most accurate at-home method is the strip-of-paper technique. Cut a thin strip of paper or use a piece of dental floss about 6 inches long. Wrap it snugly around the base of the finger you want to size, right at the knuckle if it is larger than the base. Mark where the strip overlaps. Lay the strip flat and measure from the end to the mark with a ruler. That measurement is your inside circumference. Enter it above in inches and the converter does the rest. A flexible cloth tape measure also works: note the measurement in inches at the overlap point.

How the conversion works

Ring sizes in different countries are each anchored to the inside diameter of the ring in millimetres. The US / Canada system uses a number scale where each half-size step equals roughly 0.4 mm of diameter (about 1.3 mm of circumference). The UK / Australia system uses letters with half-step suffixes. European and French sizes equal the inside circumference in millimetres rounded to the nearest whole or half number. Japanese sizes follow a similar but not identical numbering. German sizes equal the inside diameter in millimetres rounded to one decimal place. This converter measures circumference or diameter, converts to mm, finds the nearest entry in the ISO 8653 international reference table, and returns the corresponding size in each system.

Tips for accurate sizing

Finger size can vary by half a size or more depending on temperature, time of day, and hydration. Fingers are largest in the evening and when warm, and smallest in the morning and when cold. Measure at the end of the day when your fingers are at their largest to avoid buying a ring that is too tight. If you are between two sizes, size up for comfort if the band is wide (6 mm or wider), because wide bands feel tighter than the same diameter in a thin band. For non-resizable metals such as titanium, tungsten, and cobalt chrome, getting the size right before ordering is especially important.

Ring size systems around the world

The United States and Canada use a numerical scale running from size 1 (about 11.6 mm diameter) to size 16 (about 23.8 mm diameter), with half-size increments. The United Kingdom, Ireland, Australia, and New Zealand use an alphabetical scale from A through Z with additional half and numbered suffixes beyond Z. Continental Europe and France use a scale equal to the inside circumference in millimetres, so a 50 mm circumference is a European size 50. Japan uses a numerical scale that starts slightly differently from the US scale and does not have half-size steps for all sizes. Germany measures the inside diameter in millimetres directly. This converter handles all five systems from a single measurement.