The essentials

An adult has about 70 mL of blood per kilogram of body weight: around 5 liters (10 US pints) for 154 lb. About 55% is plasma, mostly water; the rest is red cells, white cells and platelets. Your volume is not on a routine report, but your complete blood count shows what your blood is made of.

How many liters of blood are in the human body?

In adults of normal weight, blood volume averages about 70 mL per kilogram[7]. For a person who weighs 70 kg (154 lb), that makes about 4.9 liters: roughly 10.4 US pints, or 1.3 gallons. The exact amount depends on height, weight and sex, which a classic hospital formula combines[8]. With it, a man who is 5 ft 9 in (1.75 m) and weighs 165 lb (75 kg) has about 5.0 liters, and a woman who is 5 ft 4 in (1.62 m) and weighs 132 lb (60 kg) has about 3.7 liters.

Weight alone can mislead: the amount per kilogram falls as weight rises, so the 70 mL/kg rule overestimates the volume of people with obesity[7][9]. Note that 1 mL is the same as 1 cc; see what cc means in medicine.

What is blood made of?

Blood has a liquid part, plasma (water, salts and proteins), and a solid part: red blood cells, white blood cells and platelets[1]. About 55% is plasma and 45% is cells[2].

What a typical 5 liters of adult blood contains
ComponentShare and contentMain job
PlasmaAbout 55% (2.75 L). Itself 92% water, 7% proteins such as albumin, 1% salts, sugars, fats, hormones and vitamins[2]Carries cells and salts; holds blood pressure and volume[2]
Red blood cellsAbout 5 million per microliter[11]Carry oxygen from the lungs to the organs[1]
White blood cells4,500 to 11,000 per microliter[4]Fight infection; part of the immune system[1]
Platelets150,000 to 400,000 per microliter[4]Help blood clot[1]

The bone marrow makes these cells all the time. Red cells live about 120 days, platelets about 6 days, and some white cells less than a day[1]: about 5 million old red cells are cleared every second[11]. Plasma proteins appear on lab reports as albumin and total protein.

Where does my lab report show what my blood is made of?

A routine report never gives your blood volume. It shows the makeup of your blood through the complete blood count (CBC), which measures red cells, white cells, platelets, hemoglobin and hematocrit[4]. Here is a fictitious US report for an adult woman.

Fictitious example of a lab report line (United States format)
TestResultReference rangeFlag
RBC (red blood cell count)5.3 x10^6/µL4.2-5.4-
Hemoglobin15.9 g/dL12-16-
Hematocrit49 %36-48H
WBC (white blood cell count)6.8 x10^3/µL4.5-11.0-
Platelet count245 x10^3/µL150-400-
  1. Hematocrit: the share of your blood volume taken up by red cells, the rest being plasma[5]. Here, 49% of the blood is red cells. Read more about your hematocrit result.
  2. Flag H: just above the range. Dehydration is a common reason: less plasma makes red cells look more concentrated[5].
  3. RBC and hemoglobin: see what your hemoglobin means and the red blood cell count.
  4. WBC and platelets: counts of white blood cells and platelets, written in thousands per microliter.
  5. Reference range: it varies between labs; the one on your report prevails[4].

A flag on your hematocrit, hemoglobin or red cell count and no idea what it means? BloodSense reads your whole report line by line and helps you prepare questions for your doctor.

Get my blood count explained

How much blood do men, women, children and babies have?

Babies have less blood in total, but more per kilogram than adults. These are averages; your doctor's estimate prevails.

Typical blood volume by age and situation
PersonBlood volumeExampleSource
Preterm newbornAbout 100 mL/kgA 3.3 lb (1.5 kg) baby: about 150 mLChooi 2026[12]
Full-term newbornAbout 90 mL/kgA 7.7 lb (3.5 kg) baby: about 315 mL, a little over a cupChooi 2026[12]
Older child70-80 mL/kgA 55 lb (25 kg) child: about 1.75 to 2 LChooi 2026[12]
Adult of normal weightAbout 70 mL/kg154 lb (70 kg): about 4.9 LLemmens 2006[7]
PregnancyAbout 45% more than before pregnancyAbout 1,200 to 1,600 mL extraSoma-Pillay 2016[10]

In pregnancy, plasma grows faster than red cells. Hemoglobin, hematocrit and the red cell count therefore fall a little, even in a healthy pregnancy[10].

What makes blood volume or blood makeup too low or too high?

A high hematocrit often means missing plasma rather than too many red cells. From the most frequent causes to the rarest:

  • Common Dehydration from severe diarrhea, heavy sweating or water pills: less plasma, so a higher hematocrit and red cell count[4]. See dehydration signs and causes.
  • Common Bleeding, visible or hidden, which lowers the hematocrit[5]; a long-term loss often ends in iron deficiency.
  • Possible Anemia from low iron, folate or vitamin B12, chronic illness or chronic kidney disease[5]; see our guide to anemia symptoms and causes.
  • Possible Smoking, high altitude, testosterone, or heart or lung disease with low oxygen, which can raise red cells[4].
  • Rare Polycythemia vera, a bone marrow disease that makes too many red cells, or a kidney tumor that produces too much erythropoietin[4][5].

Low blood volume lowers blood pressure: see low blood pressure causes and tests.

How much blood can you lose?

A blood donation takes about a pint[3], close to a tenth of an adult's blood. Plasma is replaced within about 24 hours, red cells in four to six weeks, hence at least 56 days between whole blood donations[3].

Doctors grade sudden bleeding by the share of blood lost: under 15% causes little reaction; 15-30% speeds up the heart; 30-40% is critical, organs start to lack blood; over 40% means profound shock needing immediate treatment[13]. For an adult with 5 liters, 30% is about 1.5 liters.

What can skew my hematocrit and hemoglobin before a blood test?

No fasting is needed for a CBC[4], but these results depend on the balance between plasma and cells. Tell your doctor about:

  • Recent dehydration: vomiting, diarrhea, a hot day, intense sport or water pills[4].
  • A recent trip or move to high altitude: the hematocrit rises for several weeks[5].
  • A blood donation in the last 4 to 6 weeks, or recent bleeding[3].
  • Pregnancy[10], smoking or testosterone treatment[4].
  • A large amount of IV fluid, for example during a hospital stay: too much water in the body lowers the hematocrit[5].

More tips are in our guide to what to expect at a blood draw.

When should I see a doctor about blood loss or a high hematocrit?

When to see a doctor

  • Emergency: call 911 for heavy bleeding that does not stop, vomiting blood or black stools with dizziness, fainting, a racing heart, cold and clammy skin or confusion.
  • Within 24 to 48 hours if you feel unusually tired, pale or short of breath, or your hemoglobin or hematocrit is far outside the range.
  • At your next appointment if a hematocrit slightly above or below the range was found by chance and you feel well.

Questions to ask your doctor

  1. Is my hematocrit high because I was dehydrated, or should it be repeated?
  2. Are my hemoglobin and red cell count consistent with anemia?
  3. Could a medicine or altitude explain these results?
  4. Is it safe for me to donate blood, and how often?

Frequently asked questions

Can a test measure exactly how much blood I have?

Yes, but it is a specialized test, not a routine one. A specialized lab measures red cell mass and plasma volume with radioactive tracers, then compares them with reference ranges based on body surface area[9].

Does my blood type change how much blood I have?

No. Your blood type (A, B, AB or O, Rh positive or negative) matters for transfusions and pregnancy[1]; the amount of blood depends on your height, weight and sex[8]. Read how to read a blood type test.

How often can I donate blood?

Whole blood can be given every 56 days, up to 6 times a year, if you weigh at least 110 lb and are in good health[6].

  1. MedlinePlus. Blood. US National Library of Medicine. medlineplus.gov (accessed October 31, 2026)
  2. American Red Cross. Learn All About Plasma. redcrossblood.org (accessed October 31, 2026)
  3. American Red Cross. Frequently Asked Questions: Blood Donation Process. redcrossblood.org (accessed October 31, 2026)
  4. MedlinePlus Medical Encyclopedia. Complete blood count. US National Library of Medicine. medlineplus.gov (accessed October 31, 2026)
  5. MedlinePlus Medical Encyclopedia. Hematocrit. US National Library of Medicine. medlineplus.gov (accessed October 31, 2026)
  6. American Red Cross. Whole Blood Donation. redcrossblood.org (accessed October 31, 2026)
  7. Lemmens HJ, Bernstein DP, Brodsky JB. Estimating blood volume in obese and morbidly obese patients. Obes Surg. 2006;16(6):773-776. doi:10.1381/096089206777346673 (accessed October 31, 2026)
  8. Nadler SB, Hidalgo JH, Bloch T. Prediction of blood volume in normal human adults. Surgery. 1962;51(2):224-232. PMID 21936146 (accessed October 31, 2026)
  9. Pearson TC, Guthrie DL, Simpson J, et al. Interpretation of measured red cell mass and plasma volume in adults: Expert Panel on Radionuclides of the International Council for Standardization in Haematology. Br J Haematol. 1995;89(4):748-756. doi:10.1111/j.1365-2141.1995.tb08411.x (accessed October 31, 2026)
  10. Soma-Pillay P, Nelson-Piercy C, Tolppanen H, Mebazaa A. Physiological changes in pregnancy. Cardiovasc J Afr. 2016;27(2):89-94. doi:10.5830/CVJA-2016-021 (accessed October 31, 2026)
  11. Thiagarajan P, Parker CJ, Prchal JT. How Do Red Blood Cells Die? Front Physiol. 2021;12:655393. doi:10.3389/fphys.2021.655393 (accessed October 31, 2026)
  12. Chooi CSL, Simmonds MC, Fisher L, et al. Management of neonatal massive hemorrhage: A narrative review. Transfusion. 2026;66(5):1012-1022. doi:10.1111/trf.70186 (accessed October 31, 2026)
  13. Meza Monge K, Rosa C, Sublette C, et al. Navigating Hemorrhagic Shock: Biomarkers, Therapies, and Challenges in Clinical Care. Biomedicines. 2024;12(12):2864. doi:10.3390/biomedicines12122864 (accessed October 31, 2026)

This article is general information about blood volume and blood composition. It does not replace the advice of a doctor, who interprets your results with your symptoms, history and examination.