how small is an atom

An atom is extremely small, typically around 100 picometers (pm) across. To put this in perspective, a human hair is about a million carbon atoms wide, illustrating just how tiny atoms really are. The nucleus inside an atom is even smaller, about 10 femtometers (fm) in diameter, which is thousands of times smaller than the atom itself. Atoms are so small they are smaller than the shortest wavelength of visible light, making them impossible to see with regular microscopes.