The formula seems perfect to surprise: we would be ten times more bacterial than humans. But what exactly are we counting on, and on what measures is this report based? In 2016, Ron Sender, Shai Fuchs and Ron Milo took up these estimates.
For a reference man weighing seventy kilograms, their analysis estimates about 38 trillion bacteria and 30 trillion human cells. Here, a trillion means one thousand billion. The ratio is therefore close to one to one, with uncertainty and variation between individuals.
These numbers are not an exact inventory of each body. They also do not compare the masses of the two sets, and bacteria alone do not represent all microorganisms. The amazing lesson is both scientific and biological: a memorable number can travel far before someone returns to check how it was built.
What we know
Estimates for a reference individual, not personal value; human cells and bacteria, not mass or complete set of the microbiota.
To go to the source
References consulted on September 21, 2026. Linked pages may be in another language.
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