Below you can see the front view size comparison of Canon 5DS R and Nikon D850. Canon 5DS R is 8mm shorter and 3mm thinner than Nikon D850 but it is also 6mm wider.
Canon 5DS R vs Nikon D850 - Front View
Canon 5DS R vs Nikon D850 - 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