The radii of most atoms are actually measured in the Ǻ, or Angstrom. We can do it in nanometers too, however.
First, we take the radius of the smallest atom, He (Helium). Atomic radius = .031 nm. The largest atom, stable atom is Fr (Francium), with atomic radius = .27 nm.
Therefore, the typical atomic radius is between .031 and .27 nm.