The average adult human body contains between 1.2 and 1.5 gallons of blood. Since there are 128 ounces in a gallon, the average adult has between 153 and 192 ounces of blood in their body.
How Much Blood is in the Human Body on Average?
The amount of blood in the human body depends on several factors like age, sex, size, and overall health. Here is a quick overview of the average blood volume for different groups:
- Newborn baby: 275 mL or 10 oz
- Child aged 5: 1.5 L or 51 oz
- Teenager: 4-5 L or 135-170 oz
- Adult man: 5-6 L or 170-204 oz
- Adult woman: 4-5 L or 135-170 oz
As you can see, newborns and children have less blood volume than adults. Blood volume increases rapidly during growth spurts in adolescence.
Adult males tend to have more blood than females on average due to having larger bodies and more muscle mass. Elite athletes may have up to 1.5 gallons or 204 oz of blood.
Blood Composition
Human blood is made up of plasma, red blood cells, white blood cells, and platelets. Here is the typical breakdown:
- Plasma – About 55% of blood is plasma. Plasma is the liquid portion of blood that suspends the cells and helps transport nutrients and waste.
- Red blood cells – About 44% of blood volume consists of red blood cells. These cells contain hemoglobin which carries oxygen.
- White blood cells – Only about 1% of blood is made up of white blood cells. These cells fight infection.
- Platelets – Less than 1% of blood volume is made up of cell fragments called platelets. They help blood clot.
This composition varies slightly between individuals but plasma and red blood cells account for the vast majority of the blood in healthy humans.
Functions of Blood
Blood has three main functions within the human body:
- Transport – Blood transports oxygen, carbon dioxide, nutrients, hormones, and waste throughout the body. The plasma acts as the transport fluid while the red blood cells carry oxygen.
- Regulation – Blood helps regulate body temperature, pH, and water content of cells. Proteins and salts in the plasma help maintain homeostasis.
- Protection – The white blood cells and platelets in blood help protect the body from disease and infection. They also help repair injuries by clotting blood.
Without blood to perform these critical functions, cells would quickly die and the body would be unable to sustain itself.
Where is Blood Located in the Body?
Blood circulates through an interconnected network of arteries, veins, and capillaries. Here is how blood flows through the body:
- Blood starts its journey by being pumped out of the heart through the main artery called the aorta.
- It then flows into smaller arteries that lead to every organ and tissue in the body.
- The smallest blood vessels are tiny capillaries where oxygen and nutrient exchange occur with cells.
- Capillaries connect to small veins that lead blood back to the heart.
- The right side of the heart pumps blood to the lungs to release carbon dioxide and pick up oxygen.
- The newly oxygenated blood returns to the left side of the heart to begin circulation again.
Although blood flows everywhere, the majority is stored in the heart, lungs, veins, arteries, and capillary networks. Significant volumes are also present in the liver, spleen, kidneys, and bone marrow.
Blood Volume Changes
Even though we have a relatively fixed volume of blood, the amount in various areas of the body can change temporarily. Here are some factors that influence blood volume distribution:
- Posture – Blood pools more in the legs and arms when sitting or standing vs. lying down.
- Digestion – More blood flows to the digestive system during digestion.
- Exercise – Physical activity redirects blood to muscles and skin.
- Stress – Stress hormones cause vessels to constrict, increasing blood to vital organs.
- Dehydration – Fluid loss reduces overall blood volume.
- Pregnancy – A women’s blood volume increases by 30-50% to support the fetus.
Despite these shifts, the body maintains tight control over blood pressure and flow thanks to the nervous and endocrine systems.
Measuring Blood Volume
There are several ways to measure blood volume in the body:
- Complete blood count (CBC) – This common blood test gives red blood cell, white blood cell, and platelet counts which can indicate blood volume status.
- Blood pressure – Low blood pressure can signal reduced blood volume.
- Heart rate – An increased heart rate compensates for lower blood volume.
- Blood tests – Levels of albumin and hemoglobin in the blood also correlate with volume status.
- Dye indicator dilution – Injecting a known amount of dye into the bloodstream can help quantify total blood volume.
Doctors monitor blood volume closely in surgical patients, trauma victims, and individuals at risk of significant blood loss.
Typical Blood Volume by Age and Sex
Here is a table summarizing the average total blood volume for humans by age and biological sex:
| Age Group | Male | Female |
|---|---|---|
| Newborn | 10 oz | 10 oz |
| 1-6 years | 32-65 oz | 32-65 oz |
| 6-12 years | 65-100 oz | 65-100 oz |
| 12-17 years | 100-150 oz | 100-120 oz |
| Adult | 160-240 oz | 120-160 oz |
As shown, males tend to have higher blood volume compared to females. Blood volume peaks by the late teenage years and young adulthood. It then remains relatively stable throughout adulthood.
Changes in Blood Volume
There are several conditions that can lead to abnormal increases or decreases in total blood volume:
- Hemorrhage – Major blood loss from trauma reduces blood volume. This requires emergent transfusion.
- Burns – Severe burns result in fluid shifts and lower blood volume.
- Dehydration – Vomiting, diarrhea, and excessive sweating deplete fluid from the blood.
- Pregnancy – Blood volume can increase up to 50% more than normal.
- Kidney disease – Certain conditions cause fluid retention, increasing blood volume.
- Cancer – Some cancers increase blood cell production and blood volume.
- Heart failure – Fluid buildup in the circulatory system expands blood volume.
- Infection – Severe infections make vessels leaky, leading to fluid and blood loss.
Doctors monitor blood volume closely when patients experience any of these conditions. Intravenous fluids or blood products may be given to restore normal blood volume.
Ideal Blood Volume Range
For good health, it’s ideal to maintain blood volume within the normal range. Here are target ranges by age and sex:
| Age Group | Male | Female |
|---|---|---|
| 1-6 years old | 32-65 oz | 32-65 oz |
| 6-12 years old | 65-100 oz | 65-100 oz |
| 12-17 years old | 100-150 oz | 100-120 oz |
| Adult | 160-240 oz | 120-160 oz |
Values outside the normal range may indicate an underlying problem requiring treatment. Maintaining ideal blood volume is important to ensure adequate circulation and blood pressure.
Conclusion
In summary, the average adult human has between 160-240 ounces of blood if male, and 120-160 ounces if female. Babies start with around 10 ounces of blood at birth, increasing to adult volumes by adolescence as they grow. Blood volume is tightly regulated by the circulatory system but can fluctuate temporarily based on position, activity, and overall health status. Deviations outside the normal blood volume ranges often signify disease or blood loss requiring medical treatment. Checking typical blood markers like haemoglobin provides insights into an individual’s blood volume status.