Below you can see the front view size comparison of Panasonic S1 and Sony A9. Sony A9 is clearly the smaller of the two cameras. Its body is 22mm narrower, 14mm shorter and 34mm thinner than Panasonic S1.
Panasonic S1 vs Sony A9 - Front View
Panasonic S1 vs Sony A9 - 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