How to measure your ring size
Take a well-fitting ring and measure the diameter of the inside of your ring. This is your ring size.
For example: Size 18 corresponds with a diameter of 18 mm.
Use a flexible measuring tape to measure the circumference of your finger. If you don't have a measuring tape, use a piece of paper or string, no thicker than 0.5 mm, and then measure the length of the paper / string with a ruler. This is the circumference of your finger.
Use the following ring size converter chart below to determine your ring size. Look at circumference mm.