A normal follicle size is approximately 0.71 to 0.94 inch. The follicle is a cavity inside of the ovary that contains an egg. During ovulation, the follicle grows until it is 0.71 to 0.94 inch and then ruptures, completing ovulation.
Follicle size is typically measured using an ultrasound. When women undergo fertility treatments, an ultrasound is used to determine if their follicles are reaching the appropriate size before rupture. Ultrasounds can also be used after the administration of fertility drugs to see when the follicles have reached a normal size. Follicles that do not grow large enough do not release fertile eggs and complete ovulation.