Below you can see the front-view size comparison of the Nikon D5300 and Olympus E-M10 II. The Olympus E-M10 II is clearly the smaller of the two cameras. Its body is 5 mm narrower, 15 mm shorter and 29 mm thinner than the Nikon D5300.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.