Two easy ways to measure
You can size a ring from either measurement:
- Finger circumference: wrap a thin strip of paper or string snugly around the base of your finger, mark where it overlaps, and measure the length in millimetres.
- Ring diameter: take a ring that already fits and measure straight across the inside, from edge to edge, in millimetres.
Circumference and diameter are linked by a circle's geometry (circumference = π × diameter), so either one gives your size.
How the systems relate
EU (ISO 8653) ring sizes are simply the inside circumference in millimetres, which makes them the most intuitive. US sizes use a numeric scale and UK sizes use letters, this tool maps your measurement to all three.
Tips for an accurate fit
- Measure at the end of the day, when fingers are at their largest.
- Avoid measuring when cold, fingers shrink and you'll size too small.
- Go up a size for wide bands (4 mm+), which fit more snugly.
- The ring should slide on easily but need a gentle push over the knuckle.