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How many atoms are in the human body?

Answer 1

Would you settle for a whole bunch? I didn't think so. The number of atoms in one person is almost too big to write out. But fortunately there's a shorthand system, called scientific notation, that we use instead for writing really BIG or really SMALL numbers. Since huge numbers are generally just estimates anyway, we just use the first few numbers, followed by a code that tells you how many zeros would follow if you wrote it all out. Ok, here it goes. Hydrogen, oxygen and carbon make up about 99% of the average human. I'm going to cheat a little and leave out the other 1%, which is made up of trace elements (that is, stuff there's only a trace of in the body). Then, let's assume an average adult weighs 70 kilograms. Be sure to keep in mind that the following numbers are based on the number of atoms, not percent of body weight (by weight we are mostly oxygen). A 70 kg body would have approximately 7*1027 atoms. That is, 7 followed by 27 zeros:


Of that, 4.7*1027 would be hydrogen atoms, which have one proton and one electron each. Another 1.8*1027 would be oxygen, which has 8 protons, 8 neutrons and 8 electrons. There are 7.0*1026 carbon atoms, which have 6 protons, 6 neutrons and 6 electrons. Now, let's add that all up:


Well, you'll have to agree that really is a whole bunch.

Answer 2

As they say in French - "Beaucoup," meaning a lot! A very technical, but very interesting, discussion of this can be found at In summary, for a typical human of 70 kg, there are almost 7*1027 atoms (that's a 7 followed by 27 zeros!) Another way of saying this is "seven billion billion billion." Of this, almost 2/3 is hydrogen, 1/4 is oxygen, and about 1/10 is carbon. These three atoms add up to 99% of the total!

The web site gives a detailed list of the all the different kinds of atoms making up the human body (there's even some uranium in us!) More importantly, this site is an introduction to a very new area of medical research named Nanomedicine which can be defined as "the monitoring, repair, construction and control of human biological systems at the molecular level, using engineered nanodevices and nanostructures." Anyone who has watched the Star Trek TV shows has certainly come across this idea in some of the "Borg" episodes.


Answer 1 - Brian Kross, Chief Detector Engineer (Other answers by Brian Kross)

Answer 2 - Brian Kross, Chief Detector Engineer (Other answers by Brian Kross)

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