Below you can see the front view size comparison of Pentax 645Z and Nikon Z 7. Nikon Z 7 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 Z 7 - Front View
Pentax 645Z vs Nikon Z 7 - 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