Below you can see the front view size comparison of Fujifilm X-T3 and Nikon Z7. Fujifilm X-T3 is clearly the smaller of the two cameras. Its body is 1mm narrower, 8mm shorter and 9mm thinner than Nikon Z7.
Fujifilm X-T3 vs Nikon Z7 - Front View
Fujifilm X-T3 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