Below you can see the front view size comparison of Pentax 645Z and Nikon Z7. Nikon Z7 is clearly the smaller of the two cameras. Its body is 22mm narrower, 16mm shorter and 55mm thinner than Pentax 645Z.
Pentax 645Z vs Nikon Z7 - Front View
Pentax 645Z vs Nikon Z7 - Top View
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.
Camera Size Comparison
Select Two Cameras for Size Comparison