A woman is said to be have menorrhagia if the menstrual blood loss is MORE than:

Menorrhagia is defined as loss more than 80 ml of blood per cycle and frequently producing anemia. Predictors of menorrhagia includes bleeding resulting in iron deficiency anemia or a need of transfusion, passage of clots more than 1 inch diameter and changing pad or tampon more than hourly. Normal menstrual bleeding last for an average of 5 days with a mean blood loss of 40 ml. Menorrhagia is defined as bleeding between periods. Polymenorrhea is defined as bleeding that occurs more often than every 21 days. Oligomenorrhea is defined as bleeding that occur less frequently than every 35 days. Ref: Konkle B. (2012). Chapter 58. Bleeding and Thrombosis. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.