How Much Blood Is in the Human Body?
Medically reviewed by Jeffrey S. Lander, MD
The amount of blood in the human body varies based on age, weight, and sex. An adult male weighing about 200 pounds can have almost 6 liters, or a little over 12 pints, of blood while an adult female weighing about 165 pounds might have 4.3 liters, or about 9 pints, of blood.
The body can manage some blood loss without difficulty. Once blood loss is faster than the body can replace it, the body can go into shock.
This article will detail the amount of blood typical by age and sex, how much blood can be lost and the effects of blood loss, how the body replaces lost blood, and how blood volume affects diagnosis and treatment.
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Terminology
In this article, "male" and "female" refer to people assigned those sexes at birth. Differences in blood volume appear to be determined by anatomic, hormonal, and chromosomal characteristics present at birth. Verywell Health recognizes that people may have a gender identity that varies from this definition.
Amount of Blood in Body by Age and Sex
Blood volume varies from person to person. How much you weigh, your age, and your sex are all factors that determine an adequate blood volume.
Generally, typical amounts of blood are:
Adult male weighing about 200 pounds and at about 6 feet tall has an estimated 5.7 liters (5,700 milliliters), or 12 pints, of blood volume (an average 75 milliliters per kilogram).
Adult female weighing about 165 pounds and about 5 feet 5 inches tall has an estimated 4.3 liters (4,300 milliliters), or 9 pints, of blood volume (an average 65 milliliters per kilogram).
An infant has about 1.2 fluid ounces of blood volume for every pound of body weight, or 75 to 85 milliliters of blood per kilogram.
A child has about 1 to 1.2 fluid ounces of circulating blood for every pound of body weight, or 70 to 75 milliliters of blood per kilogram.
The sex difference in blood volume is largely due to males having more lean body mass compared to more adipose (fat) tissue in females.
How Much Blood Can the Body Lose?
Given the importance of blood volume in transporting oxygen and nutrients throughout the body, regulating temperature, and protecting the body, blood loss should be evaluated by a healthcare provider.
For minimal blood loss, the body can usually replace the blood volume without much impact. Larger losses of blood volume can be a medical emergency and require lifesaving interventions such as a blood transfusion.
The American College of Surgeons developed criteria to classify blood volume loss. This classification was developed based on an otherwise healthy 70 kilogram, or 154-pound, individual. The various classes of blood loss also include signs and symptoms that are likely to be present:
Class 1: Class 1 occurs when 15% or less (approximately 750 milliliters) of blood volume is lost. Heart rate might increase slightly, and there is often no change in blood pressure or breathing rate.
Class 2: Class 2 happens when blood loss is more than 15% but less than 30% (approximately 750 to 1,500 milliliters). Often, heart rate and breathing rate are elevated, and blood pressure might start to decrease.
Class III: Blood volume loss greater than 30% but less than 40% (approximately 1,500 to 2,000 milliliters) usually causes large decreases in blood pressure, and a person's mental status, such as alertness and ability to converse, starts to decline. Heart rate and breathing rate are much higher than normal ranges as well. Capillary refill times increase, too. (It takes longer for the smallest blood vessels to refill with blood.)
Class IV: When blood volume loss is over 40%, or more than 2,000 milliliters, blood pressure becomes very low, heart and breathing rates are very high, and a person's mental status becomes confused, irritable, and possibly unconscious. Capillary refill times are very long as well.
Testing a blood sample in the laboratory is often done to help determine the extent of blood loss. The primary laboratory value utilized to determine the amount of blood volume loss is hemoglobin. Hemoglobin is an important protein carried by the blood's red blood cells and transports oxygen throughout the body.
Hemoglobin levels vary based on sex:
Male: For an adult male, a normal hemoglobin range is 13.5 to 17.5 grams per deciliter.
Female: For an adult female, a normal hemoglobin range is 12.0 to 15.5 grams per deciliter.
The Association for the Advancement of Blood & Biotherapies (AABB) worked with a panel of experts to recommend that if hemoglobin levels drop below the acceptable range and the individual with a low hemoglobin is having symptoms as described above, a healthcare provider can consider many treatment options, including a blood transfusion.
Blood Loss Treatment Options
Several interventions can help stop blood loss. Applying direct pressure to the wound, pressure above the wound with a tourniquet, or use of medications specifically designed to increase clotting are all methods that can be used to stop bleeding.
Intravenous fluids or plasma transfusion may help stabilize blood volume if it has dropped significantly.
Blood transfusion may be needed if hemoglobin levels drop too low. This may be a whole blood transfusion or a packed red blood cell transfusion. Component transfusion of platelets may also be needed.
How Does the Body Make More Blood?
The bone marrow makes blood cells, a process called hematopoiesis. Stem cells in the bone marrow differentiate to produce the cellular components of blood:
Red blood cells: Red blood cells carry hemoglobin, a protein that delivers oxygen to cells and removes carbon dioxide waste.
White blood cells: White blood cells help protect the body from infections from bacteria, viruses, or other foreign invaders.
Platelets: Platelets are an important part of the body's clotting process, which is needed to help prevent blood loss.
Peritubular cells in the kidneys are sensitive to oxygen levels in the blood. If the cells sense a decrease (such as due to blood loss), they secrete the hormone erythropoietin. This signals the bone marrow to make more red blood cells.
Iron is needed to produce hemoglobin in red blood cells, so the body taps into iron stores and increases the amount it absorbs from the diet.
Other chemical messengers in the body signal the bone marrow to produce more platelets and white blood cells when they are low.
However, it takes weeks for the marrow to replace any cellular component. If blood loss is too rapid, a transfusion may be needed.
Plasma is the liquid part of blood. When blood is lost, plasma is replenished from the body's store of liquid. If blood volume is lost, fluids need to be replaced (orally or intravenously) to restore plasma levels. The kidneys also respond to reduce the loss of fluids and maintain plasma volume.
Plasma is replaced relatively rapidly in the body. For example, a person can donate plasma twice weekly, as long as there are 48 hours between donations.
Related: Why Do People Need Blood Transfusions?
Using Blood Volume to Arrive at a Diagnosis
Determining blood volume status can be an important part of a healthcare provider's ability to make a diagnosis and determine the most effective treatments. Blood volume can be important in various diseases, such as shock due to blood loss or decompensated heart failure.
Blood volume assessment can involve:
Physical examination: Involves assessment of things like skin turgor, dryness of mucous membrane, dizziness when standing, low blood pressure, or high pulse rate. This method is non-invasive but lacks the accuracy of specific blood volume levels.
Hemoglobin and hematocrit: These two blood tests can be rapidly performed by the lab or within an emergency room. Hematocrit is the percentage of red cells in the blood.
More specialized methods include:
Internal monitoring of the blood vessels: A pulmonary artery catheter, also called a Swan-Ganz catheter, is inserted into large blood vessels leading into and out of the heart and lungs. This catheter can measure different pressures in the blood vessels and determine if blood volume is too low or too high.
Nuclear medicine blood volume analysis: This is a specialized method of directly assessing blood volume using a nuclear medicine machine. The technique is minimally invasive but does have small amounts of radiation associated with the testing process. This method of blood volume analysis used to take four to six hours, but newer techniques can complete testing within 90 minutes or less.
Summary
Blood volume varies based on age. weight and sex. An adult male who is about 6 feet tall and weighs about 200 pounds has about 12 pints of blood. The bone marrow produces the cellular components of blood—red blood cells, white blood cells, and platelets.
Medical interventions, such as blood transfusions, might be needed if bleeding reduces blood volume significantly, which can produce shock. Laboratory testing and physical examination can determine the extent of blood loss and what interventions are needed.
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