Ring Size Calculator

Wrap a thin strip of paper or a piece of string snugly around the base of your finger, mark where it overlaps, then measure that length in millimeters with a ruler. That number is your inner circumference. Enter it in the calculator and switch the input type to finger circumference (mm). Measure at the end of the day when your fingers are slightly larger, and never when your hands are cold.

Measure the inside diameter of that ring with a ruler or caliper, edge to edge, in millimeters. Choose inner diameter (mm) as the input type and enter the value. A typical women's ring runs 16 to 17 mm and a typical men's ring runs 19 to 20 mm. Diameter is more precise than tracing the ring on paper because the line thickness throws off the measurement.

US sizes are numeric, and this calculator accepts 0 to 16 with half sizes. Its reference table covers US 3 to 14 and uses the Howard linear step outside that table. UK sizes use letters, EU sizes follow inner circumference in whole millimeters, and Japanese sizes use a separate numeric chart. Treat every cross-system result as a starting point because manufacturers can use different tolerances.

Yes. Bands wider than about 6 mm sit on more skin and feel tighter at the same nominal size. Most jewellers recommend going up by a quarter to a half US size for bands 6 to 8 mm wide, and a full half size for anything wider. If you live somewhere hot or your fingers swell from exercise or salt, lean toward the larger half size shown in the recommended fit.

Finger circumference can vary 0.3 to 0.5 mm across a day from temperature, hydration, salt intake, exercise, and hormonal cycles, which is roughly a third of a US size. Cold weather shrinks fingers, heat and salty meals enlarge them. Measure two or three times across different days and use the largest reading so a permanent ring still fits when your hands are warmest.