Ring Size Calculator

• The large headline size is your best-match US/Canada size, alongside the measured or derived inner diameter and circumference in millimeters.
• The International equivalents table converts that same physical size into every other supported system side-by-side, so you don't need to re-enter your measurement for each one.
• Results from the "have a ring" and "measured my finger" modes are always labeledEstimated — they're derived from a real-world measurement, which always carries some margin of error, unlike a size you already know exactly.

When this happens, the calculator shows both the nearest smaller and nearest larger standard size instead of silently rounding to one. As a general guide: for thinner bands (roughly under 6mm wide), sizing down to the nearer size is usually comfortable; for wider bands, many jewelers recommend sizing up, since a wide band contacts more of the finger and can feel tighter than a thin band at the same nominal size. If you're unsure, a local jeweler can size you precisely in person.

• Fingers are typically larger later in the day and in warm weather, and smaller in the cold — measure a few times if you can.
• Wider bands fit more snugly than thin bands at the same nominal size.
• Different jewelers and manufacturers can reference slightly different sizing standards, especially between countries.
• When measuring an existing ring, always measure the inside diameter — measuring the outside of the band will give you a size that's too large.

View the full ring size chart →