animated text. Text: How much blood is lost during a period? According to the Centre for Menstrual Cycle and Ovulation Research, the average length of menstrual bleeding is four to six days. Although the amount of blood loss varies person-to-person, it's typically about 10 to 35 ml. Sometimes it seems like a lot of blood, but don't fret - any blood that you lose is quickly replaced by the blood-forming cells in your body.
