To measure your hand circumference
you need a pen, paper band and a ruler.

A ruler band is perfect but a paper band will do it as well.

It’s not easy to do that by your own so maybe you need one more hand.
Just mark the overlap with a pen.

circumference   -      bangle size
(cm/inch)     -       diameter
19      -      62
20      -      64
21      -      66
22      -      68
23      -      70