Below you can see the front-view size comparison of the Panasonic FZ300 and Olympus E-M10 II. The Olympus E-M10 II is clearly the smaller of the two cameras. Its body is 12 mm narrower, 9 mm shorter and 70 mm thinner than the Panasonic FZ300.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.