The average adult has about 4.5 to 5.5 liters of blood circulating inside their body. Human blood is consist of three main components that is erythrocytes (red blood cells, RBCs), leukocytes (white blood cells , WBCs), and thrombocytes (platelets). By volume, RBCs constitute about 45% of whole blood,, WBCs about 0.7%. and the plasma about 54.3% respectively.