According a study from Washington University, there are approximately 100 trillion atoms in a human cell. Approximately the same number of cells are in the entire human body, meaning that 10 octillion atoms, or a 1 followed by 28 zeros, make up each person.
The 100 trillion figure is a close approximation for the number of atoms in a cell, but there are many reasons that it is not an exact figure. Among other variables, human cells attain vastly different sizes. For example, blood cells are a few micrometers in diameter, while neurons can be up to 0.1 millimeters in length.