The total number of octahedral void (s) per atom present in a cubic close packed structure is:

The closed packed structure have both octahedral and tetrahedral voids. In a ccp structure, there is one octahedral void on the edge. Each one of which is common to four other unit cells. Thus, in cubic close packed structure,
Octahedral voids in the centre of the cube = 1
Effective number of octahedral voids located at the
$12\text{ edge of cube }=12\times \frac{1}{4}=3$
$\therefore$ Total number of octahedral voids = 4