What is atomic size?
Atomic size is how far way is the outer most electron on the the atom.
If you wanted to know what unit of measurement atoms are measured, a common one is Angstroms, which are
Depending on your knowledge level you will realize that the electron outer most ring is not a perfect circle nor is it constant depending on various conditions. Due this knowledge, there is various different measurements for the atomic size, but what is key with most of these measurements is a ratio between each atom is the same no matter the conditions in which all atoms were measure at.