One unit of blood translates to about 120 ml. A unit of blood is a suspension of red blood cells separated from 200 ml of whole blood, where its white blood cells, platelets and other substances are removed as much as possible. Its red blood cells account for about 40% to 50% of the whole blood, so a unit of aqueous blood solvent is about 80 to 100 ml, and at the same time, other substances, such as calcium ions, anticoagulants, etc., are added, so that a unit of blood can be about 120 ml. In blood transfusion, its blood use is measured in units, and one unit of blood transfused to an anemic patient can raise the patient’s hemoglobin by about 5 to 6 grams. Clinically, it is mostly used to treat patients with severe anemia, acute blood loss and other diseases.