Below you can see the front-view size comparison of the Panasonic GH4 and Panasonic GH5S. The Panasonic GH4 is clearly the smaller of the two cameras. Its body is 6mm narrower, 5 mm shorter and 3 mm thinner than the Panasonic GH5S.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.