Below you can see the front view size comparison of Nikon P900 and Sony RX10 IV. Sony RX10 IV is 7mm narrower and 9mm shorter than Nikon P900 but it is also 8mm thicker.
Nikon P900 vs Sony RX10 IV - Front View
Nikon P900 vs Sony RX10 IV - 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