In cubic close packing, each cube consists of eight small cubic components as shown in figure. Since atoms are present in corners and face centres, total atoms are:

Total atoms= atoms at face centres and atoms at corners

=8× (1/8) + 6× (1/2)=1+3 = 4

Total number of atoms = 4.

Now octahedral voids are present at Edge centres and body centre. (refer figure)

Total number of octahedral voids =

Hence proved. 4 octahedral voids are present in cubic close packing.