The average uterine lining thickness on day 14 of a woman's menstrual cycle is 6 to 8 millimeters, according to the International Asherman's Association. During this time, the egg releases from the dominant follicle and travels down the Fallopian tube in a process known as ovulation.
The uterine lining, also known as the endometrium, thickens during the proliferative phase of a woman's cycle, notes Our Bodies, Ourselves. The estrogen from the ovarian follicle causes the uterine lining to grow to so that a fertilized egg has a chance to implant. This thickening typically lasts about six to 20 days. If implantation does not occur, the uterine lining begins to shed on day 28 and continues to do so for about five to seven days, notes the International Asherman's Association.