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I recently came across this fact:

There's enough DNA in the human body to stretch from the sun to Pluto and back.

A couple of "Bollocks!" alarms began to chime in my head. While I expect that it will stretch a long way, Pluto seemed a little far-fetched. Looking this up further led me to this page which actually calculates the figure in some detail. The final result came to around 2x1013 metres or ~134AU.

In the interest of keeping things manageable, I'm going to use AU from here on in.

Discover Magazine might be the source of the Pluto analogy:

Don’t try this at home: If uncoiled, the DNA in all the cells in your body would stretch 10 billion miles—from here to Pluto and back.

10B miles = 10B * 1.62 / 150M = 108AU

The mean distance between Pluto and the Sun = 39AU. Distance between the Earth and Pluto and back = (39 - 1) * 2 = 76AU

Another page claims:

If you could unwrap the DNA you have in all the cells in your body, you would be able to reach the moon and back 6,000 times. This would be a distance of:

384000 * 2 * 6000 = 4608M Km ~= 31AU

Unless my calculations are ridiculously flawed, something is amiss here. While I'm flabbergasted that just the DNA in a human body can stretch to, well, almost three times the distance of Pluto from the Sun, it appears that most, if not all these analogies are incorrect. So, my question is: If all the DNA in an adult human body were to be uncoiled and stretched out, how long would it actually stretch for?

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    Well, the first page you linked gives the correct figure (with refs) of (length of 1 bp)(number of bp per cell)(number of cells in the body) ~= 2.0 × 10^13 meters, what is wrong with that?
    – nico
    Aug 25, 2012 at 22:13
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    There doesn't seem anything 'amiss' here at all. All of the estimates are within an order of magnitude. Your main estimate suggests the human body has 10^13 cells which is only one order of magnitude precision AND is going to vary greatly between individuals. There is no contradiction to explain.
    – Oddthinking ♦
    Aug 26, 2012 at 1:54
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    @nico I'm sceptical of the result, not just the math. And I found that the result of the math varies widely. But I'm now a little more comfortable with this fact as I've realised that if I stretched myself out atom to atom, I could reach the edge of the Milky Way :o
    – user7920
    Aug 26, 2012 at 19:11
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    I would like to remark that these numbers do not really convey anything, since the average layperson has no grasp about the distance between the Sun and Pluto (besides "very far") or the amount of cells in a human body ("many"). More useful is the information calculated by @Sklivvz: One strand of DNA uncoiled ≈ 2 meters. That should be enough to blow some minds.
    – Twinkles
    Mar 18, 2014 at 10:45

2 Answers 2

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Data

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

—Wolfram Alpha

The haploid human genome (23 chromosomes) is estimated to be about 3.2 billion base pairs long.

—Human Genome – Wikipedia

The full DNA content of a cell is therefore 6.4 Gbp.

Average base pair size: one bp corresponds to approximately 3.4 Å of length along the strand

—Base Pair – Wikipedia

Average Pluto distance from Earth: 6.09×1012 meters

—Wolfram Alpha

Average Pluto distance from Sun: 6.09×1012 meters

—Wolfram Alpha

Note: Why are these basically the same distance? Think about it: 50% of Earth's orbit is behind the Sun so it adds to the distance, but the other 50% the Earth is in front of the Sun so it subtracts. On average, it's a very similar distance.

A Pluto round trip is approximately: 1.2×1013 meters

Average Moon distance from Earth: 3.85×108 meters

—Wolfram Alpha

A Moon round trip is approximately: 7.7×108 meters

Calculation

Total length of DNA in 1 cell:

6.4×109 × 3.4×10-10 meters ≈ 2 meters

Total length of DNA of all cells in human body:

2 meters × 1014 = 2×1014 meters

The total length of the DNA strands in the human body in units of Pluto roundtrips is:

2×1014 meters / 1.2×1013 meters/Pluto roundtrip ≈ 17 Pluto roundtrips

10 billion miles are 1.6×1013 meters (assuming statute miles for "miles" – you never know exactly with uncommon units)

The total length of the DNA strands in the human body in units of 1x1010 statute miles is:

2×1014 meters / 1.6×1013 meters/1010 statute miles ≈ 12×1010 statute miles

The total length of the DNA strands in the human body in units of Moon roundtrips is:

2×1014 meters / 7.7×108 meters/Moon roundtrip ≈ 2.6x105 Moon roundtrips

Claims verification

There's enough DNA in the human body to stretch from the sun to Pluto and back.

True. It can be done 17 times

If uncoiled, the DNA in all the cells in your body would stretch 10 billion miles—from here to Pluto and back.

Incorrect. Surely the DNA would stretch 10 billion miles (which is approximately the distance to Pluto and back). However it would do so 12 times.

If you could unwrap the DNA you have in all the cells in your body, you would be able to reach the moon and back 6,000 times.

Incorrect. You would be able to do so 260,000 times, not 6,000.

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  • Can someone please verify the data and calculations?
    – Sklivvz
    Aug 26, 2012 at 14:42
  • I've not et checked them all. But, an initial look suggests that your result differs from the "Steven Chen" result listed in my post by exactly 10. Any idea why?
    – user7920
    Aug 26, 2012 at 19:14
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    @col I've asked on bio.se
    – Sklivvz
    Aug 26, 2012 at 19:36
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    Of note: not all human eukaryotic cells contain DNA (the notable exception being Red Blood Cells, which lose their nucleus during maturation from its stem cell). And an average human has approximately somewhere between 2E13 and 3E13 human blood cells source. So that might change these numbers, but without running through them I don't think it changes the result.
    – Jimmy M.
    Mar 27, 2017 at 15:46
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    Which of these calculations include mitochondric DNA, the DNA of enterobacteria, and the DNA of whatever pathogens the human in question might have in his organism at the time of measurement? ;-)
    – DevSolar
    Mar 28, 2017 at 7:39
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@Sklivvz posted a good back of the envelope theoretical answer, but it is off by a factor of 10 for the following reason:

An estimation of the number of cells in the human body Annals of Human Biology (2013) finds that the number of cells in the human body is:

3.72 × 1013 of which 2.63 × 1013 are erythrocytes (red blood cells which do not have DNA) and 1.45 × 1012 are platelets (which do not have chromosomal DNA).

So the best estimate is 9.5 × 1012 cells with chromosomal DNA.

According to Lehninger Principles of Biochemistry the length of DNA in a diploid human cell is 2 meters.

So the total length of cellular DNA in human is 1.9 × 1013 meters.

This is about 3 times the distance to Pluto, the distance to Pluto averaging 6.1 × 1012 meters.

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  • I don't like this idea of multiplying it by the number of cells, it just means you are repeating the same thing over and over again. Also it gives bulkier people an advantage, if they can increase their body weight faster than their Telomeres deteriorate.
    – daniel
    May 15, 2017 at 13:45
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    @Daniel "for the purposes of this work we chose a 30-year old young adult, weighing 70 kg" is what the paper says
    – DavePhD
    May 15, 2017 at 13:48

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