How Many Atoms There Are in the Human Body

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 percent of the atoms in the body are hydrogen or oxygen. Carbon, hydrogen, nitrogen, and oxygen together account for 99 percent 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 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