Answer – The body of an average adult human has about 4.7 to 5.7 liters (1.2 to 1.5 gallons) of blood.

Explanation: 

Blood is an essential fluid that circulates throughout the human body to distribute vital nutrients and oxygen as well as carry metabolic waste away. It is primarily composed of red blood cells, white blood cells, and platelets in a liquid plasma.

Blood can neither be replaced nor can it be made outside the body. However, the development of synthetic substitutes is being researched and is a work in progress. The amount of blood in the human body is thus limited. It is usually equivalent to 7–8% of a person’s body weight and can vary further based on age and gender:

• Newborns have about 75 mL of blood per kg of body weight. So a baby weighing approximately 3 kg (≈7 pounds) is likely to have around 225 mL (0.6 gallons) of blood.
• A pre-teen child weighing 40 kg (≈90 pounds) will have about 3 liters (0.8 gallons) of blood.
• An average adult human with a weight of 63–77 kg (140–170 pounds) will have 4.7–5.7 liters (1.2–1.5 gallons) of blood.

Due to menstruation, women usually have lower blood volumes than men. However, pregnant women have anywhere between 30%–50% more blood than non-pregnant women. This is approximately 1.1–1.5 liters (0.3–0.4 gallons) more.

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