We suggest two simple methods to find the perfect size for you.
First method:
Make a complete circle around your finger with a thread (consider the center of the first phalanx as a reference), mark with a pen the point where it crosses, lay the thread parallel to a ruler and you will get your circumference.
Second method:
Measure the diameter of one of your rings with a ruler. Be careful to measure from inner wall to inner wall at the widest part.