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How many human cells are there in our body, on average?

Wikipedia says 1013:

Bacterial cells are much smaller than human cells, and there are at least ten times as many bacteria as human cells in the body (approximately 1014 versus 1013).

The Nobel site says 1014:

An adult human being has approximately 100 000 billion cells, all originating from a single cell, the fertilized egg cell.

The Physics fact book insists it's 1013:

(length of 1 bp)(number of bp per cell)(number of cells in the body)
(0.34 × 10-9 m)(6 × 109)(1013)

Finally, Wolfram Alpha gives 1.0 × 1014 as fact:

Estimated number of eukaryotic (human) cells in the human body: 1.0×1014

I am quite confused: who is right here?

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Well, the Nobel quote is wrong whichever way you turn it (for the reason outlined in the Wikipedia quote). But I wouldn’t be surprised that, even taking the average, there’s an uncertainty of a factor 10 about the correct number. Because all the factors used to determine the number are crude estimates indeed. –  Konrad Rudolph Aug 26 '12 at 19:50
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In Mike Lynch's "The Origins of Genome Architecture", he claims 10^13. I forget the primary source he cited, and since the book is in my office I can't check it now.

** Found the snippet that contained the reference. I think it's really worth including in its entirety.

A crude estimate of the amount of DNA within currently living organisms can be made by noting that the length spanned by one base of DNA is ~0.3x10^-12 km (Cook 2001).

The number of viral particles in the open oceans is ~10^30 (Suttle 2005). Assuming that there are twice as many viruses on land and in fresh water does not change the global estimate very much at the order-of-magnitude level. Thus, assuming an average viral genome size of 10^4 bp, the total length of viral DNA if all chromosomes were linearized and placed end to end is ~10^22 km.

The estimated global number of prokaryotic cells is ~10^30 (Whitman et al. 1998), and assuming an average prokaryotic genome size of 3x10^6 bp yields an estimated total DNA length of 10^24 km.

With a total population size of 6x10^9 individuals, 10^13 cells per individual (Baserga 1985), and a diploid genome size of 6x10^9 bp, the amount of DNA occupied by the human population is ~10^20 km. Assuming there are ~10^7 species of eukaryotes on Earth (~6 times the number that have actually been identified), that the average eukaryotic genome size is ~1% of humans, and that all species occupy approximately the same amount of total biomass, total eukaryotic DNA is ~10^5 times that for humans, or ~10^25 km.

Given the very approximate nature of these calculations, any one of these estimates could be off by one or two orders of magnitude, but it is difficult to escape the conclusion that the total amount of DNA in living organisms is on the order of 10^25 km, which is equivalent to a distance of 10^12 light years, or 10 times the diameter of the known universe.

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