An endometrial thickness of 1.6cm is normal. A normal endometrial thickness of approximately 4-18mm is considered normal. The endometrial thickness of 1.6cm generally suggests that the endometrial thickness may be measured by ultrasound before menstruation. The thickness of the endometrium is influenced by many factors. The endometrium is at its thinnest during menstruation, around 4mm. With the onset of the menstrual cycle, ovulation of the ovaries and changes in hormone levels, the endometrium gradually thickens, reaching 8mm by the time of ovulation. before menstruation, the endometrium may reach 18mm, so the thickness of the endometrium is 16mm, which is the normal endometrium if it is before menstruation. If it is just after menstruation, that is, when the follicular growth period endometrium of 16mm, it is abnormal.