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A quick Google search didn't turn up any reliable sources. An awkward Cosmoquest thread gives a rough estimate of 10^25 to 10^32, but this is just a bad extrapolation of the number of cells in a human body. Also, I recently learned that we don't even know the number of cells in humans to good precision.

Has anyone ever made a serious attempt to figure this out? If not, does anyone here want to make a quick calculation?

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  • $\begingroup$ Do you want to count human cells, animal cells or really ALL cells (including bacteria & archea), because these are different orders of magnitude & difficulty $\endgroup$
    – Nicolai
    Commented Jun 15, 2017 at 4:11
  • $\begingroup$ @Nicolai All cells, anywhere and in any organism. $\endgroup$
    – StarlightDown
    Commented Jun 15, 2017 at 4:12
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    $\begingroup$ I'm voting to close this question as off-topic because it relates to the Guinness book of records, not biology. $\endgroup$
    – David
    Commented Jun 15, 2017 at 10:09
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    $\begingroup$ @another'Homosapien' — A manner of speaking. You might also term it a "Freak Show" question. This sort of question is asked for no reason other than to be able to respond "wow". It is the very antithesis to science. $\endgroup$
    – David
    Commented Jun 15, 2017 at 12:30
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    $\begingroup$ I disagree strongly with the people saying this is off-topic, or that it is simply a "wow-factor" question. I think knowing at least an estimate of the number of cells on Earth is important to understanding the environment we live in and just how rare multicellular life is. $\endgroup$
    – Bryan Krause ♦
    Commented Jun 15, 2017 at 16:07

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Okay so I looked around a bit, and there are surprisingly few papers related to this question.

This paper is the best I cold find, but it's almost 20 years old. There's also this one, which slightly updates the other one, but they both focus on bacteria. For those the total number is estimated to be somewhere in the range of $10^{30}$.
For humans the latest published number is $3.72 \times 10^{13}$, so even with a few billion in total ($10^9 \times 10^{13} = 10^{22}$) we probably don't even matter for the total cell count. Since smaller more abundant animals have a much lower number of cells, they probably don't matter either.

Now to the only thing I'm not sure about: plants

The number of plants on earth is really elusive, only more elusive is the number of cells per plant. This study claims around 3 trillion ($10^{12}$) tree's on earth. Since tree's are bound to have (many) more cells than humans, we're probably getting closer to the number of prokaryotic cells by now (I guess the number of 'tree cells' will be somewhere around $10^{27} - 10^{30})$.
So far I didn't find anything about grasses or other plants (neither numbers nor cell counts), so it's really hard to say whether these matter or not.
This study seems to give an average number of cells per growth ring in tree's, but I'm not sure how to get a number of cells / tree from that.

In total the estimated number of bacteria ($10^{30}$) is probably a good measure for the number of cells on earth. Even if plants manage to come to that level, the order of magnitude will probably not change (by much).

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    $\begingroup$ It doesn't seem that surprising to me that there are few papers on unanswerable trivia. $\endgroup$
    – canadianer
    Commented Jun 15, 2017 at 5:08
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About $10^{30}$ prokaryotes (Whitman et al. 1998).

It is an extremely vague estimates of course! Not that every eukaryotic cell contain about $10^3$ mitochondria, so of course eukaryotic cells would have to be negligible in counts even if you consider only the mitochondria. I don't know if Whitman et al. 1998 counted bacteria but it does not change much given the accuracy of their estimate.

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    $\begingroup$ $10^7$ is way to low for the number of eukaryotic cells. There are ~7 billion ($10^9$) humans on earth, and we definitely have a large number of cells to multiply with that. $\endgroup$
    – Nicolai
    Commented Jun 15, 2017 at 4:47
  • $\begingroup$ Very minor edit suggest: proCaryotes would be proKaryotes . I could not save the suggested edit because the warning message tells "edit must be 6 character at least. Is there anything else to improve?" Spaces are not getting counted. I don't really have anything else to improve. $\endgroup$
    – user25568
    Commented Jun 15, 2017 at 6:00
  • $\begingroup$ Thanks for your help. Indeed, $10^7$ was an estimation of the number of species from M. Lynch. I rewrote the number without thinking. I removed the estimate. $\endgroup$
    – Remi.b
    Commented Jun 15, 2017 at 14:01
  • $\begingroup$ Thanks for your help. Indeed, $10^7$ was an estimation of the number of species from M. Lynch. I rewrote the number without thinking. I removed the estimate. $\endgroup$
    – Remi.b
    Commented Jun 15, 2017 at 14:01

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