Below you can see the front view size comparison of Nikon D4s and Nikon D810A. Nikon D810A is clearly the smaller of the two cameras. Its body is 14mm narrower, 34mm shorter and 9mm thinner than Nikon D4s.
Nikon D4s vs Nikon D810A - Front View
Nikon D4s vs Nikon D810A - 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