20. According to the information of 14 ring, 14 ring needs 20 red diamonds, 14 ring has a diameter of 17.2mm and a circumference of 54 mm.14 ring size is the ring size worn by most women, which corresponds to the unique ring diameter and circumference. However, the size standard of 14 ring is different in different countries and even among jewelry brands, and some countries don't even have the size of 14 ring.