The NaCl structure can be thought of as a face centred cubic array of Cl^- ions with Na⁺ ions occupying the octahedral holes.

Both Na⁺ and Cl^- ions are 6 coordinate

The unit cell contains

[1+{12x(1/4)} = 4 Na⁺ ions and

[{8x(1/8)}+{6x(1/2)}] = 4 Cl^- ions