Biology
How many atoms are in the human body?
~7 × 10²⁷ atoms
How many atoms are in the human body?
The average 70 kg human body contains approximately 7 × 10²⁷ (seven octillion) atoms — mostly hydrogen (60%), oxygen (26%), and carbon (11%). These atoms are constantly recycled: some of the atoms in your body were once inside stars, oceans, dinosaurs, and historical figures. The oxygen you just inhaled was probably exhaled by millions of people before you.
Source: Freitas (1999) Nanomedicine; basic physics calculations