Below you can see the front-view size comparison of the Nikon P7800 and Olympus E-M1 II. The Nikon P7800 is clearly the smaller of the two cameras. Its body is 15mm narrower, 13 mm shorter and 17 mm thinner than the Olympus E-M1 II.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.