According to the University of North Carolina Medical School, the average woman loses around 40cc, or 3 tablespoons, of blood during her period. Heavy periods are considered to be any amount of blood loss over 80 cc, or 5 tablespoons.
Mayo Clinic states that a normal menstrual cycle occurs every 21 to 35 days, and lasts anywhere from 2 to 7 days. As a woman begins to menstruate, her periods are longer than those experienced by older women and come at varying times each month. However, as women age, their menstrual cycles should become more regular each month. The average menstrual cycle for older women is 28 days.