How Many Atoms Are in the Human Body?

Atoms in the Body

Scientist analysing molecular model in laboratory
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Have you ever wondered how many atoms are in the human body? Here's the calculation and answer to the question.

Short Answer

There are approximately 7 x 1027 atoms in the average human body. This is the estimate for a 70 kg adult human male. Generally, a smaller person would contain fewer atoms; a larger person would contain more atoms.

Atoms in the Body

On average, 87% of the atoms in the body are hydrogen or oxygen.

Carbon, hydrogen, nitrogen, and oxygen together account for 99% of the atoms in a person. There are 41 chemical elements found in most people. The exact number of atoms of the trace elements varies widely according to age, diet, and environmental factors. Some of these elements are needed for chemical processes in the body, but others (e.g., lead, uranium, radium) have no known function or are toxic contaminants. Low levels of these elements are a natural part of the environment and typically do not cause health problems. In addition to the elements listed in the table, additional trace elements may be found in some individuals.

Reference: Freitas, Robert A., Jr., Nanomedicine, http://www.foresight.org/Nanomedicine/index.html, 2006.

Atomic Composition of a Lean 70-kg Man

Element# of Atoms
hydrogen4.22 x 1027
oxygen1.61 x 1027
carbon8.03 x 1026
nitrogen3.9 x 1025
calcium1.6 x 1025
phosphorus9.6 x 1024
sulfur2.6 x 1024
sodium2.5 x 1024
potassium2.2 x 1024
chlorine1.6 x 1024
magnesium4.7 x 1023
silicon3.9 x 1023
fluorine8.3 x 1022
iron4.5 x 1022
zinc2.1 x 1022
rubidium2.2 x 1021
strontium2.2 x 1021
bromine2 x 1021
aluminum1 x 1021
copper7 x 1020
lead3 x 1020
cadmium3 x 1020
boron2 x 1020
manganese1 x 1020
nickel1 x 1020
lithium1 x 1020
barium8 x 1019
iodine5 x 1019
tin4 x 1019
gold2 x 1019
zirconium2 x 1019
cobalt2 x 1019
cesium7 x 1018
mercury6 x 1018
arsenic6 x 1018
chromium6 x 1018
molybdenum3 x 1018
selenium3 x 1018
beryllium3 x 1018
vanadium8 x 1017
uranium2 x 1017
radium8 x 1010