How to find bangle size ?

Your hand size, not your wrist, determines the size of your bangle. Simply tuck your thumb into the palm of your hand (as if you were about to put on a bangle) and use tailor's tape to measure your hand from knuckle to knuckle around the set of knuckles closest to your wrist.

How to find ring size?

The diameter is the measurement across the inner width of the ring when determining a ring size. Use a ruler or tape measure to measure the inside of the ring from edge to edge at its widest points. For the most accurate measurement of their ring size, try to use a circular ring if at all possible.