Use experimental measurements from X-ray diffraction, electron diffraction, or spectroscopy
Determine the distance between nuclei of two bonded identical atoms
Divide that internuclear distance by 2 to get the atomic radius
For nonbonded atoms, use van der Waals distances and divide by 2
For metallic atoms, use the distance between neighboring atoms in the metal lattice and divide by 2
For covalently bonded atoms, use the covalent bond length and divide by 2
For ionic atoms, use ionic radii tables based on the ion’s charge and coordination number
Compare the atom’s value with standard atomic radius data from chemistry reference tables
Use periodic trends if an exact measured value is not available
Apply the appropriate radius type: covalent radius, metallic radius, van der Waals radius, or ionic radius