An adult typically has about 5 liters of blood in the body, but this amount can vary depending on a person’s body weight. In general, the lower the body weight, the smaller the total blood volume tends to be.
For individuals who weigh less than 110 lbs (about 50 kg), even a relatively small amount of blood loss (like the 450 mL usually collected during a blood donation) can be significant. In these cases, the risk of side effects like dizziness, nausea, or fainting may be higher.
To ensure safety, one of the main requirements for blood donation is usually a minimum body weight of over 110 lbs.