How Many Atoms are There in Our Body?

How many atoms are there in an average human adult body?

Firstly, we make some approximations.

The 3 major elements that make up our body are Hydrogen, Oxygen and Carbon. Through chemical bondings they can form various compounds such as Glucose and Carboxylic Acids (Example: Fatty Acids).

For your information, these 3 elements make up 99% of our body atoms.

So here we neglect the 1% and make it into 100%.

Hydrogen atoms make up 7.804532657kg of our body.

7.804532657kg X Avogadro Constant X 10^3(kg to g)
= 7.804532657kg X 6.0221415 X 10^23 X 10^3
= 4.7 X 10^27

There are 4.7 X 10^27 Hydrogen Atoms in our body.

Oxygen atoms make up 23.91175963kg of our body.

23.91175963kg / Molecular Mass X Avogadro Constant X 10^3(kg to g)
= 23.91175963kg / 16g X 6.0221415 X 10^23 X 10^3
= 1.8 X 10^27

There are 1.8 X 10^27 Oxygen Atoms in our body.

Carbon atoms make up 13.94852645kg of our body.

13.94852645kg / Molecular Mass X Avogadro Constant X 10^3(kg to g)
13.94852645kg / 16g X 6.0221415 X 10^23 X 10^3
= 7.0 X 10^26

There are 7.0 X 10^26 Carbon Atoms in our body.

Thus, in total, there are approximately :
Number of Hydrogen Atoms + Number of Oxygen Atoms + Number of Carbon Atoms
= 4.7 X 10^27 + 1.8 X 10^27 + 7.0 X 10^26
= (4.7 + 1.8 + 0.7) X 10^27
= 7.2 X 10^27

There are approximately 7.2 X 10^27 Atoms in our body!!!


  1. there should be a constant in front of your answer with such calculation. human mass varies from one body to another.

    be more scientific la.

  2. lol. i also know there's somthing wrong with this. We're using Average Mass of Human, that's 80kg. But after calculation I found that the total weight is just 50+kg, So I just don't use the constant haha. Instead of categorizing this post as "Science Study", I've changed it to "Funny Stuffs" lol.