According to LifeStream, an average child who weights 40 pounds has around 2 to 3 pints of blood. Scientists estimate, on average, that blood makes up about 7 percent of a person's total weight, regardless of age.
LifeStream says that a 110-pound teenager has around 7 pints of blood. When donating blood, each pint of blood is separated into three primary components: red blood cells, plasma and platelets. Each component is used in different situations. For example, red blood cells are needed for surgery patients and accident victims. The plasma from the blood is used for burn, shock and organ transplant patients. Platelets are needed when treating cancer or leukemia patients.