The follicle development on the 11th day of the menstrual cycle is about 15*15mm, which is considered normal, but the exact size of the follicle development varies from one person to another due to differences in the menstrual cycle. Generally speaking, if the menstrual cycle is 28 days, then the ovulation period is on the 14th day of menstruation, the 11th day of menstruation follicle development is about 15mm is normal, if there is no dominant follicle development on the 11th day of menstruation, then consider the possibility of endocrine dysfunction, you need to the first day of the menstrual period, fasting blood test for hormone six to determine the cause of the measures taken to treat the cause. If the menstrual cycle is irregular for more than 30 days, then the ovulation period is 14 days before the next menstrual period, then the follicle can develop into a dominant follicle on the 11th day of menstruation. If you want to prepare for pregnancy, it is recommended to monitor follicular development with intermittent vaginal ultrasound to ensure that the follicles are mature enough to have intercourse in time for a better chance of pregnancy.