The size of a cobalt atom is typically measured by its atomic radius, which is the distance from the center of the nucleus to the outermost electron shell.

The atomic radius of cobalt is about 125 picometers (pm), which is equivalent to 0.125 nanometers (nm).

However, it's important to note that the atomic radius can vary depending on the specific chemical environment in which the cobalt atom is found. For example, the atomic radius of cobalt in a metallic solid will be different from the atomic radius of cobalt in a gaseous state.

Here's a breakdown of the size in different units:

* Picometers: 125 pm

* Nanometers: 0.125 nm

* Angstroms: 1.25 Å

* Meters: 1.25 x 10^-10 m

Keep in mind that atoms are incredibly small, and even the smallest visible particles are still millions of times larger than a single atom.