How Much Blood Is In Your Body?

We've often heard that our bodies are made up of mostly water as a way to encourage us to drink more water. According to Medical News Today, our bodies are made up of about 45 to 75% water, depending on our age, gender, body composition, and size. Have you ever thought about why we're made up of mostly water? Well, one of the reasons that we need water is so that our bodies can make blood. Your blood is made up of 50% water, and blood plasma is made up of 92% water (via Medical News Today).

Blood in the human body carries out several important tasks — regulating body temperature, forming clots, moving oxygen to cells — that are crucial for your survival (via WebMD). If you lose too much blood through pregnancy, injury, severe burns, vomiting, or even diarrhea, your body may go into hypovolemic shock, a life-threatening emergency. If you lose over 30% of your blood volume, you will most likely need a blood transfusion. So how much blood does your body need for daily function and survival?

The amount of blood depends on gender, height, and weight

Just as with water content, the amount of blood in the human varies from person to person. For example, a 165-pound woman of average height has about 4.3 liters of blood circulating throughout her body, but a pregnant woman's blood volume can increase by 50 percent of that amount. A 200-pound male of average height has a blood volume of 5.7 liters, while a 60-pound child has a blood volume of about 2 liters (via Medical News Today).

Certain health conditions can have an effect on how much blood is in your body. The medical terms for decreased blood volume and increased blood volume are hypovolemia and hypervolemia, respectively ("Physiology, Blood Volume," 2021). Although bleeding is the most common cause of hypovolemia, it can be caused by losing too much water due to excess urination, sweating, vomiting, or dehydration (via Verywell Health). According to the book, "Physiology, Blood Volume," failure of the kidneys, heart, and liver can excessively increase blood volume in the body. While multiple systems in the body work together to regulate the amount of blood in our bodies, the amount of water is the primary regulator of blood volume.