Anatomy

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How Much Blood Is Circulating in Your Body?

Last Modified Date: February 28, 2024

As humans, we tend to take things for granted – starting with our own bodies. The human body is a miraculous and complex system made up of organs, tissues, bones, veins, arteries, plasma, blood, and so much more. Most of our body parts are critical for our survival, yet we don't think about them much – unless something goes wrong.

For example, have you ever wondered how much blood is circulating in your body? The average adult has around five liters (1.3 gallons) of blood, which accounts for around 10% of their weight. And while a human infant only has about as much blood as a 10-pound (4.54-kg) cat (roughly one cup, or 0.2 liters), a six-year-old child has about the same amount of blood as an adult. However, due to their smaller size, a child's blood accounts for a much greater proportion of their body weight than an adult's.

The average adult has around 5 liters of blood circulating in their body, accounting for around 10% of their weight.

It is estimated that someone in the U.S. needs a blood transfusion every two seconds, which makes giving blood critical – especially for individuals with rare blood groups. There's a good reason, though, why you can't donate a pint of blood (0.57 liters) every day, or even every week. Though new red blood cells are constantly being made in the bone marrow, it can take up to six weeks for your blood to fully regenerate after a donation.

It's all in the blood:

Various factors can affect the quantity and composition of your blood, including your location. At high altitudes, your body will produce more red blood cells because there is less oxygen available. And during pregnancy, a woman's blood volume increases by 30 to 50 percent to support her growing fetus.

Human blood is made up of plasma, red and white blood cells, and platelets, along with dissolved electrolytes and nutrients that are transported around the body.