Below you can see the front view size comparison of Nikon P1000 and Sony A6400. Sony A6400 is clearly the smaller of the two cameras. Its body is 26mm narrower, 52mm shorter and 121mm thinner than Nikon P1000.
Nikon P1000 vs Sony A6400 - Front View
Nikon P1000 vs Sony A6400 - 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