The volume of 2 units of blood is about 200-220ml, because 1 unit of blood is the red blood cells extracted from 200ml of whole blood, which is about between 80-90ml. After the red blood cells are extracted, appropriate anticoagulant is added, and the volume of each unit of blood is about between 100-110ml, and the volume of 2 units of blood is about between 200-220ml. The patient’s hemoglobin concentration is increased by about 10 g/L when 2 units of blood are injected at the same time. Depending on the degree of anemia and the volume of blood input, it is possible to deduce the degree of hemoglobin increase after transfusion. In patients with acute blood loss, the amount of blood loss can also be inferred approximately from the hemoglobin concentration after blood loss.