You can determine the size of your Ring using the methods stated below. 

METHOD 1
Put a ring on a circle that you are most suited. Make sure that the line is inside the ring, not outside. If you choose between two sizes, choose the larger size.

METHOD 2
Take a piece of thread and double check that it is not stretched or tangled. Also Cut piece of paper width of 3-4 mm. Wrap it around your fingers for a snug diligence, it does not tighten it too much.
Take a pen or pencil and mark the point on the string where the match takes place.
Attach a thread to the strip and define its size. If you choose between two sizes, choose the larger size.

METHOD 3
Print and cut dimensional tape loop
Make a slit in the line
Twist the ring as shown in the figure
Put tape on the finger and pull the latch so that the paper tightly adjacent to the finger
look at extreme figure.

Another question that probably faced you or your loved ones: A perfect fit ring suddenly become too big or not small. This is natural: people lose weight or get better, and change the size of a finger. Do Not be discouraged - ring can be stretched or compressed.
This procedure is performed in almost all the jewelry shops and its cost is not high. Many ring can be compressed and stretched without harming the form. If the ring has an insertion procedure is complicated by the fact that the stone should be further strengthened in the frame. But for a qualified jeweler is not difficult. The problem occurs only when the ring has an engraving, since it can be irreversibly damaged.