How much blood is in the human body?
An average adult has about 5 liters (about 1.3 gallons) of blood. The amount depends on body size; blood makes up roughly 7 to 8 percent of body weight.
Blood is made of plasma, a yellowish liquid that is mostly water, and cells. Red blood cells carry oxygen, white blood cells fight infections and platelets help blood clot. Plasma makes up a little over half of the blood's volume.
The heart pumps the entire volume of blood around the body about once a minute at rest. Larger people have more blood, and men usually have a bit more than women of the same size. A newborn baby has only about 0.25 liters.
Donating blood
A standard blood donation is about 470 milliliters, roughly a tenth of an adult's blood. The body replaces the plasma within a day or two and the red blood cells within several weeks. Donated blood is used in surgeries, after accidents and for patients with blood disorders.
Did You Know?
If all the blood vessels in an adult body were laid end to end, they would stretch roughly 100,000 kilometers, enough to circle the Earth more than twice.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.