What is the number of Tetrahedral Void in CCP 3D structure?

To be precise, if in a close packed structure
(ccp or fcc) there are
n atoms or ions then the number of octahedral voids and tetrahedral voids will be n and 2n respectively.

In a ccp or fcc , there are 4 atoms per unit cell , Therefore Zeff (n)= 4
Therefore , Number of tectrahedral voids
= 2×zeff
= 2×4
= 8
Number of octahedral voids = Zeff
= 4