How Many Cells Are In Your Body?

A simple question deserves a simple answer. How many cells are in your body?

Unfortunately, your cells can’t fill out census forms, so they can’t tell you themselves. And while it’s easy enough to look through a microscope and count off certain types of cells, this method isn’t practical either. Some types of cells are easy to spot, while others–such as tangled neurons–weave themselves up into obscurity. Even if you could count ten cells each second, it would take you tens of thousands of years to finish counting. Plus, there would be certain logistical problems you’d encounter along the way to counting all the cells in your body–for example, chopping your own body up into tiny patches for microscopic viewing.

For now, the best we can hope for is a study published recenty in Annals of Human Biology, entitled, with admirable clarity, “An Estimation of the Number of Cells in the Human Body.”

The authors–a team of scientists from Italy, Greece, and Spain–admit that they’re hardly the first people to tackle this question. They looked back over scientific journals and books from the past couple centuries and found many estimates. But those estimates sprawled over a huge range, from 5 billion to 200 million trillion cells. And practically none of scientists who offered those numbers provided  an explanation for how they came up with them. Clearly, this is a subject ripe for research.

If scientists can’t count all the cells in a human body, how can they estimate it? The mean weight of a cell is 1 nanogram. For an adult man weighing 70 kilograms, simple arithmetic would lead us to conclude that that man has 70 trillion cells.

On the other hand, it’s also possible to do this calculation based on the volume of cells. The mean volume of a mammal cell is estimated to be 4 billionths of a cubic centimeter. (To get a sense of that size, check out The Scale of the Universe.) Based on an adult man’s typical volume, you might conclude that the human body contains 15 trillion cells.

So if you pick volume or weight, you get drastically different numbers. Making matters worse, our bodies are not packed with cells in a uniform way, like a jar full of jellybeans. Cells come in different sizes, and they grow in different densities. Look at a beaker of blood, for example, and you’ll find that the red blood cells are packed tight. If you used their density to estimate the cells in a human body, you’d come to a staggering 724 trillion cells. Skin cells, on the other hand, are so sparse that they’d give you a paltry estimate of 35 billion cells.

So the author of the new paper set out to estimate the number of cells in the body the hard way, breaking it down by organs and cell types. (They didn’t try counting up all the microbes that also call our body home, sticking only to human cells.) They’ve scoured the scientific literature for details on the volume and density of cells in gallbladders, knee joints, intestines, bone marrow, and many other tissues. They then came up with estimates for the total number of each kind of cell. They estimate, for example, that we have 50 billion fat cells and 2 billion heart muscle cells.

Adding up all their numbers, the scientists came up with…drumroll…37.2 trillion cells.

This is not a final number, but it’s a very good start. While it’s true that people may vary in size–and thus vary in their number of cells–adult humans don’t vary by orders of magnitude except in the movies. The scientists declare with great confidence that the common estimate of a trillion cells in the human body is wrong. But they see their estimate as an opportunity for a collaboration–perhaps through an online database assembled by many experts on many different body parts–to zero in on a better estimate.

Curiosity is justification enough to ponder how many cells the human body contains, but there can also be scientific benefits to pinning down the number too. Scientists are learning about the human body by building sophisticated computer models of lungs and hearts and other organs. If these models have ten times too many cells as real organs do, their results may veer wildly off the mark.

The number of cells in an organ also has bearing on some medical conditions. The authors of the new study find that a healthy liver has 240 billion cells in it, for example, but some studies on cirrhosis have found the disease organ have as few as 172 billion.

Perhaps most importantly, the very fact that some 34 trillion cells can cooperate for decades, giving rise to a single human body instead of a chaotic war of selfish microbes, is amazing. The evolution of even a basic level of multicellularity is remarkable enough. But our ancestors went way beyond a simple sponge-like anatomy, evolving a vast collective made of many different types. To understand that collective on a deep level, we need to know how big it really is.

61 thoughts on “How Many Cells Are In Your Body?

  1. Good article. Unfortunately it misses an opportunity to point out that the 37 trillion cell number is an order of magnitude too low. It doesn’t count the microbes that are actually integral to the human body.

    [CZ: The study I’m writing about didn’t estimate the size of the microbiome. It’s only looking at human cells. I’ve added a note to make that clear.]

  2. So, where does this leave the number of microbiome cells in the human body vs. human cells? The most common previous estimate of human cells was 1 trillion. With that number, it was easy to say that the microbiome cells outnumbered our own, as the number of microbiome cells was commonly thought to be 10 trillion. If this latter estimate is still believed to be true, then does the recent estimate of the number of human cells overturn the truism that most of the cells in the human body aren’t human?

  3. It is a hard concept to visualize because #’s don’t equate with volumes. Human cells can take up a greater volume even though the microbiome has many more #’s of cells. I’d like to see not only a comparison of numbers but also a comparison of volumes.

    This is a good discussion for Mole Day (6.02 am- 6.02 pm)

  4. Thanks for a fascinating answer to a question I’ve often wondered about.

    But the philosopher in me cries for consistency. You say, “37.2 trillion cells” and then in the last paragraph you mention “some 34 trillion cells.” Don’t you want these numbers to match?

  5. I have no problem comparing estimates from 1 to 100; 37 sounds not sounds like a reasonable compromise. It’s the trillion I have a problem with imagining. For instance, if every cell has a complete copy of DNA (about 6 feet in length, stretched end to end), then just that part of our bodies would combine to a length of roughly 222 trillion feet (on the back of my envelope). That’s somewhat farther than Pluto is from the Sun. It’s not that I disbelieve this. But how do I weave these huge numbers, big or small, into my sensibilty?

    1. Hey bud. One of the key issues people dont fully understand about the nature of dna is that its typically wildly contorted and mostly inactive in eash cell. For example, skin cells need to divide at a rate differently from other cells, need to produce pigments and melanin, maintain hair follicles, and cooperate with the immunes system by helping to close injuries via platelet bonding (if the platelets didnt bond to skin cells your scab would just float in a gooey surface and fall off). In order to do this, it needs access to those parts of the dna sequence that manage these functions. but dont need to access how to produce hemoglobin, or how to firm neruonal bonds. These latter parts of the dna are actually wound up super tight and small, and sit, wasted, in your skin cells. Meanwhile, the former parts arent chemically wound (this helps prevent cells from activating unnecessary parts of the dna and causing malignant mutations), are accessible by rna strands, and this also aids in cellular division to mitigate mutations. I hope this illuminates what you’re looking for.

  6. Nice article.

    I remember reading that the number of microbes in the human gut are higher than this number?! Over 100 Trillion? ‏

  7. Incredible post. Thanks for mentioning that the microbial (including viruses) world was not included in the count.

    May I add that each cell has over a hundred thousand machines within it, including DNA, which is a molecular machine that is not alive. DNA is composed of molecules that are not alive which are composed of atoms that are also not alive.

    In actual fact, our cells are a type of cyborg (Putting a Face on Machine Mutation).

  8. Good comments on the microbiome issue. On the weight ratio, too, will that change from the 90:10 traditional estimate of human cells by weight vs. microbiome?

  9. I’m not sure if I did these calculations wrong but with the amount of mistakes DNA polymerase makes, and with the number of cells in our body 1,850,000,000,000 cells in our boys create mutated proteins (I have accounted for the fact that only 1.5% of DNA codes for proteins, the one thing I didn’t account for is the fact that most mutations don’t change the proteins at all.) If anybody has another number that would be great.

  10. According to Dredds comment, If atoms and DNA microbes are not alive, why do they die? DNA is a theorized a machine yet it has to re-create the entire human with-in the very first mother cell, which means every cell mitosis isn’t the same but ordained chronologically to complete the stages of cell life but before life begins as a baby, the sperm cell has its own mind to find the egg by competition. I believe all Cell nucleuses have their own minds via preordained DNA codes due to competition. The strangest mystery is why 50 trillion cells die instantaneously when the human dies.

  11. The linked article “results” statement calls for 3.72 X 10(13). That is far more than 37 trillion. It’s closer to 37 billion trillion trillion.

  12. Do you really know? Or were you taught what you know?
    Do you believe or do you know?
    Is your faith blind?
    Or is it bright as the sun? – Killah Priest

  13. what i find astonding, other than the fantastic number of cells, is the fact that all are similar but not one is exactly alike. all are unique. something like people

  14. The commentor who called DNA and similar molecular machines “not alive” seems to have fallen into the Trap of Vitalism – that “life” is definable as an essence separable from its components. DNA and kin are alive by being part of a living cell’s processes

  15. Excellent article; substantive and very clear. Please let’s have more from the author. 3 questions: what are the organs/body parts with the highest numbers of cells; ie. how do they rank? Is there any systemtic association between the number of cells and the complexity of task by the organ, incidence of disease etc; and is the number of cells markedly different across different age groups?

  16. And where did all those cells come from and how did they all come together and function? 0 + 0 = everything in the universe?

    “The fool says in his heart, ‘There is no God.’
    For since the creation of the world God’s invisible qualities–his eternal power and divine nature–have been clearly seen, being understood from what has been made, so that people are without excuse.
    Although they claimed to be wise, they became fools. They exchanged the truth about God for a lie, and worshiped and served created things rather than the Creator”

  17. Prakash: This is an easy one. Each microliter of blood has on average 5 million red blood cells, 7 thousand white blood cells and 300 thousand platelets. Average total blood volume is 5 L. Thus there are about 25.3 trillion (American usage) or 2.53 x 10exp13 cells in healthy human beings (this only includes circulating blood cells).

  18. 6th grade teacher: When we die do we have about the same # of cells as when we die? How does our physical growth factor in?

  19. Would you please be so kind as to provide a clear definition for a
    so-called human cell? What exactly is a human cell.
    This has been haunting me for sometime.
    Thank you.

  20. A good article, thanks, but one thing it highlights to me is the silliness of saying, as you do, that one body made up of some 3 or 4 x 10(13) cells working in complete harmony, to form one single being, evolved. The dna in each of those cells contains not only a digitally encoded design for that particular cells construction & function, but that for the whole body, as it moves through all its stages of develoment. If the universe is approx 14 billion yrs old, and the earth less than 1 billion (10(12)) , that is a huge amount of developnent per year. I believe there to be tens of megabytes of hugely clever and compact code per dna, so some intelligence had to imagine the complete design, then encode it. I think the average human prgrammer is only capable of tens of bytes of code per day, so how many days does it take for random chance to produce a million (mega, i.e. 10(6)) times that. Anyway, a biochemist estimated that, starting with the basic elements and joining them, there is only 1 chance in 10(125) that one of the protiens required to sustain life would be formed, and approximately 250 different such proteins are required, and that before the dna code can be written, and none of those chemicals and codes give life they are just required to sustain and build it, and are still there when life departs from the human body, though start breaking down (decaying) as soon as it does.
    No wonder you said it was “remarkable”, some would say that it is actually a mathematically ridiculous (prepostuous) supposition.

  21. In Nigeria here I am, we are told that there are 200 different types of cells and about 100trillion cell.So does it mean that there no universal compendium of the number of cell in human?

  22. Perhaps you can help me with a question that has been bothering me: when cells split, that presumably means dividing up the number of constituent atoms too?? Does that mean that each subsequent cell split results in cells that are less dense (i.e. have fewer atoms) and that the original cell contained all the atoms available? Or do cells absorb atoms from other substances, so that ultimately a cell split is something dictated by processes taking place at the atomic level?

  23. again….

    …Amazing Creation!..

    Pride, ego and vane glory comes first while we are alive….but the moment of truth (for all) comes at the time of death.

  24. I have one question about the total volume of blood cells. It seems like the quantity of blood in the average human would comprise about 70% of the total number of cells. Is this reasonable?

  25. Carl if you’re still following this thread could you look into the question of the number of red blood cells asked above?

    As you know mature red blood cells do not contain DNA.

    I’m attempting to estimate the number of mutations caused by normal cell metabolism in an average human body each day. There’s a fairly well established figure of 20,000 mutations per cell, per day:

    Without subtracting the red blood cells, 20,000 * 37.2 trillion = 744 quadrillion mutations that occur and are repaired in the average human body each and every day.

  26. Via pubmed references I did finally find an answer even though the full text of the paper is behind a paywall. It appears there are 2.63 x 10^13 erythrocytes. The table listing numbers for each organ is available as PDF download from this link:

    So if my math isn’t horribly wrong, that amounts to 10.9 trillion cells containing DNA, which in turn equals 218 quadrillion mutations per day in the average human.

  27. It is noted in Guyton & Hall’s physiology text book that there are about 25 trillion Red Blood Cells in human body and a total of 100 trillion cells in the whole human body.So the number 37.2 trillion cells in total human body, isn’t it a bit controversial?

  28. This would be what is known as science, @Nirmal… Not sure how Guyton and Hall arrived at their numbers, but given the roundness of those numbers, it seems like they did some of the math that was done at the beginning of this article, then rounded up. In any event, I seriously doubt they went to anything like the rigor described in this article…
    Better, more organized, methodical approaches get better results, the old answers get changed, and our picture of the universe gets a little more accurate.
    Also, it’s kind of meaningless to quibble over this number anyway, the best we will ever have is an average.

  29. Cathie, your question would be hard to answer in a numerical sense. As in we can not say a new eukaryotic cell would= half atoms of the parent cell. It is document that daughter cells are usually much smaller when they first form. They would half to be at least some what bigger since they had to pick up more mass by completing the other half of the dna strand that was split then replicated. That amongst other things a new cell copies when the parent cell splits into 2 new daughter cells. The simpler the cell the closer it would be to half its original mass. this seems to be less of the case the more complex the cell tho.

  30. I believe we are made up of about 50 to 100 trillion cells, the 35+ trillion cells count seems too conservative.

  31. One way to picture 64 trillion cells is to think that the human body is a cubic meter of cells. That cube would have 40000 cells on each axis. This gives you a clear picture how many cells there is.

    A typical computer processor has about 40000 transistors on each axis in a flat 2D surface. Add 40000 of these processors and you get the number of human cells. Ofcourse the cell is much more complex structure as a transistor.

  32. In my teaching to medical students, I have used 100 trillion cells, based on an estimate from one of Carl Sagan’s books.

    One observation makes me skeptical of the 37 trillion count. As a physician, we measure the number of red blood cells per litre of blood all the time. A typical result is 4 x 10 ^12 per litre (4 trillion per litre). The typical blood volume in an adult is 5 litres. This means we have 4 x 5 = 20 trillion red blood cells – it is hard for me to believe more than half of our body’s cells are red blood cells.

  33. Agree with Martin, other organisms have a red cell ratio of 35%-40%, making the total number of cells in humans more likely 70-80 x10^12.
    I would add that given the red cells, plus the platelets, and the number of external skin cells, the majority of cells in the body lack a nucleus, giving one pause about what a “typical” cell looks like…

  34. There are 53 trillion cells in a human body. And its not the scientists of Italy, Spain etc who proved it. Google for Avdhoot Baba Shivanand Ji. The holy preacher and father of Indian Healing who said there are 53 trillion cells. He has also mentioned there are 7200000 nerves in a human body which I was unware of.

  35. ‘ The evolution of even a basic level of multicellularity is remarkable enough’….
    Today, any serious biologist knows that life did not evolve. It’s an impossibility and these numbers are just one of 3.73 trillion reasons to know there is a Creator.

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