Below you can see the front-view size comparison of the Olympus E-PL9 and Panasonic GX850. The Panasonic GX850 is clearly the smaller of the two cameras. Its body is 10 mm narrower, 3 mm shorter and 6 mm thinner than the Olympus E-PL9.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.