Red blood cells are very large in number ; in women , there are 4.8 million red blood cells per microliter of blood . Adult humans have roughly 2 -- 3 1013 ( 20-30 trillion ) red blood cells at any given time , comprising approximately one quarter of the total human body cell number ( women have about 4 to 5 million erythrocytes per microliter ( cubic millimeter ) of blood and men about 5 to 6 million ; people living at high altitudes with low oxygen tension will have more ) . Red blood cells are thus much more common than the other blood particles : there are about 4,000 -- 11,000 white blood cells and about 150,000 -- 400,000 platelets in each microliter of human blood .