Most adults have about 5 liters of blood in their body, a little more than 1 gallon. The exact amount varies. Body size, weight, age, sex, and pregnancy can all affect blood volume.
Blood carries oxygen and nutrients to tissues, removes waste, helps fight infection, and helps stop bleeding after an injury.
How much blood does the average adult have?
For a healthy adult, blood volume is often estimated at about 70 milliliters per kilogram of body weight. That means blood makes up roughly 7% of body weight in many adults.
A person who weighs 70 kilograms, or about 154 pounds, may have close to 5 liters of blood.
This is only an estimate. Height, body build, muscle mass, body fat, and hydration can change the amount. 1
How many liters of blood are in men and women?
Adult men often have more blood than adult women because they tend to have a larger body size and more lean body tissue.
A typical adult woman may have around 4 to 5 liters, while a typical adult man may have around 5 to 6 liters. These are general ranges, not fixed numbers.
Body size is usually more useful than sex alone when estimating blood volume.
How much blood does a child have?
Children have less total blood than adults because their bodies are smaller. Yet children often have more blood per kilogram of body weight.
Young children may have about 80 to 90 milliliters of blood per kilogram. Infants may have even more per kilogram.
For example, a 20-kilogram child could have roughly 1.6 to 1.8 liters of blood.
Doctors use weight-based estimates in children because even a small amount of blood loss can be serious in a smaller body.
Does pregnancy increase blood volume?
Yes. Blood volume rises during pregnancy to support the baby and placenta and help prepare the body for blood loss during childbirth.
By later pregnancy, blood volume can be much higher than it was before pregnancy. Medical references report that it may rise by about 50% in some women.
This increase is a normal part of pregnancy.
What is blood made of?
Blood has two main parts: plasma and blood cells.
Plasma is the liquid portion. It carries water, proteins, hormones, nutrients, and waste products.
Blood cells include red blood cells, white blood cells, and platelets. Red blood cells carry oxygen. White blood cells help fight infection. Platelets help form clots when bleeding occurs.
Plasma makes up a little more than half of total blood volume.
How much blood can you lose before it becomes dangerous?
The effect of blood loss depends on how much is lost, how quickly it happens, and the person’s health.
A small amount, such as during a standard blood donation, is usually well tolerated by a healthy adult. Larger or rapid blood loss can cause weakness, dizziness, a fast heartbeat, pale or cool skin, confusion, fainting, and shock.
Heavy bleeding is a medical emergency. Call emergency services if bleeding will not stop, blood is pouring or spurting from a wound, or the person becomes faint, confused, very weak, or hard to wake.2
Can you calculate your own blood volume?
You can make a rough estimate by multiplying your weight in kilograms by 70 milliliters.
For example:
70 kg × 70 mL = 4,900 mL
That equals about 4.9 liters of blood.
This calculation is only a general estimate. It may be less accurate during pregnancy, in people with obesity, or when illness causes major changes in body fluids.
The bottom line
Most adults have around 5 liters of blood. A common estimate is about 70 milliliters of blood per kilogram of body weight.
Blood volume changes with body size, age, pregnancy, hydration, and some health conditions. The body keeps it within a controlled range because every organ depends on a steady blood supply for oxygen and nutrients.