Ring sizing glossary
Every sizing term, in plain English.
- Inner diameter
- The width across the inside of the ring, in millimetres. The most reliable single measurement — match an existing ring against it.
- Inner circumference
- The distance around the inside of the ring (π × diameter), in millimetres. Equal to your finger circumference for a good fit.
- US size
- A numeric system (USA, Canada, Mexico) in half-size steps, derived from inner diameter in inches: diameter = 0.458 + 0.032 × size.
- UK / AU letter
- An alphabetic scale (A–Z plus half sizes) used in the UK, Ireland, Australia, NZ and South Africa, based on circumference. US 7 = UK N½.
- EU / ISO size
- Under ISO 8653 the size number is simply the inner circumference in millimetres, so EU 54 means 54 mm around.
- Japan (JIS) size
- Japan’s own numeric scale (JIS S 4700). It has no half sizes and skips some numbers; treat conversions as approximate.
- Switzerland / Italy / Spain
- A number equal to the inner circumference in mm minus 40 (so a 54 mm circumference is size 14).
- Standard-fit
- A band with a flat inner surface. Our chart values are standard-fit.
- Comfort-fit
- A band domed on the inside so it slides on more easily; it fits about a quarter to half size larger than a standard-fit band of the same number.
- Sizing beads
- Two small beads a jeweler adds inside a band to stop it spinning, without changing the size that passes the knuckle.
- Half size
- The 0.5 step between whole sizes (e.g. US 6.5). Most fingers fall between whole sizes; when in doubt, size up.
Back to the converter or the full chart.