HOW DO I FIND THE RING NUMBER?
When trying to find the size for your ring, it would be a good idea to keep in mind that:
Your hands are probably not the same size.
Your "good" hand is usually slightly larger.
This practically means that if you know the size of a ring you wear on one hand, it may not fit on your other.
A ring is better to be a little larger than normal than smaller.
That is, if your measurement is between two numbers, it is better to choose the larger one.
Your fingers may be a little more swollen during the day or on warmer days.
Don't forget to take into account the size of the joints through which the ring will have to pass.
Below we suggest two ways to find the ring size you are interested in:
1st METHOD (Measuring the perimeter): 
Wrap a thread around your finger to create a complete circle around it.
With a pencil, mark on the tape measure or thread the point where it meets its end.
Open the tape measure or thread in a straight line (alternatively, you can use scissors to cut the thread so that the clean perimeter remains)
With a ruler, measure the length of the thread in millimeters (mm).
Record your measurement and refer to the table below to find the ring size that corresponds to your finger.
2nd METHOD (Measuring the diameter): 
If you have a ring that you already wear and are satisfied with the size, and if the ring you want to buy is for THE SAME finger, proceed with the following process:
Place the ring on a ruler or measuring tape as in the photo.
Measure the clear diameter in the middle excluding the material at the edges.
Record the measurement by measuring your length in millimeters (mm) and refer to the table below to find the ring size that corresponds to your finger.
_______________________________________________________________
Here you can watch a video that might help you.
If you are still having difficulty, you can visit a jewelry store and they will tell you the size.