The amount of blood in an adult’s body is closely related to their own body weight, because normally, the blood in an adult’s body makes up 7-8% of their whole body weight. Therefore, the amount of blood in an adult’s body is closely related to his or her own body weight, and the heavier the person, the more total blood will be in his or her body. Conversely, people who weigh less will have a corresponding decrease in the total amount of blood in their bodies. For example, a person who weighs about 60kg will have about 4200-4500ml of blood in his body. But if a person weighs about 80kg, the total amount of blood in his body is about 5500-6000ml, so the total amount of blood in an adult’s body is closely related to his own weight. Because of this, there are clear requirements for the weight of adults when donating blood in clinical settings. China’s blood donation law stipulates that adult men weighing less than 50kg and adult women weighing less than 45kg cannot donate blood.