It is estimated that between 10¹⁰ and 10¹² bacteria per 1 gram live in the colon of an average person.
To answer this question, assume that there are 10¹² bacteria per gram of human colon.
Because the average human colon weighs 220 grams, the number of bacteria in the colon is
(220 g)*(10¹² bacteria/g) = 2.2 x 10¹⁴ bacteria.
There are about 6.7 billion (6.7 x 10⁹) people on earth. Therefore the total number of bacteria in human colons is about
(2.2 x 10¹⁴ bacteria/person)*(6.7 x 10⁹ people) = 1.424 x 10²⁴ bacteria.
Answer:
About 2.2 x 10¹⁴ bacteria per person.
About 1.424 x 10²⁴ bacteria in human colons.
Note:
These answers use the upper estimate of 10¹² bacteria per gram of human colon. The lower estimate is 10¹⁰ bacteria per gram of human colon.
