Ring and Bracelet Duo.

1. Wrap a thin strip of paper or a thread around the base of your finger.
2. Mark where it meets. Keep it snug, but make sure it can slide over your knuckle.
3. Lay it flat on a ruler and measure the length in millimetres.

Measure at the end of the day, when fingers are a little bigger. If you're between two sizes, choose the bigger one.