Below you can see the front view size comparison of Nikon D3500 and Olympus E-M10 MIII. Olympus E-M10 MIII is clearly the smaller of the two cameras. Its body is 2mm narrower, 13mm shorter and 20mm thinner than Nikon D3500.
Nikon D3500 vs Olympus E-M10 MIII - Front View
Nikon D3500 vs Olympus E-M10 MIII - 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