The endometrial thickness of 1cm is normal. 1cm of endometrial thickness is usually measured clinically at the time of ovulation. endometrial thickness varies with the menstrual cycle and is generally thickest before menstruation, when it may reach 18mm or 20mm. with the onset of the menstrual cycle, the endometrium begins to peel off and the endometrium becomes thinner at this time. The thickness of the endometrium should be measured at the time of menstruation to determine if it is within the normal range. Generally speaking, if the endometrium is 1cm at the time of menstruation, this is a sign of endometrial thickening.