Find your size
The surest way is from a ring or bangle that already fits. Type the number and the size shows at once; the pages for rings and the kada add it to the bag for you.
Measuring a ring
Lay it on a ruler and read the inside width, edge to edge, in millimetres. 16.5 mm is a common size.
Thread round a finger
Wrap thread round the base of the finger, mark where it meets, and measure the length. Do it in the evening, when fingers are a little bigger.
Round a hand
Tuck your thumb into your palm as if putting a bangle on, and wrap a tape round the widest part. That's the number to type.