Below you can see the front-view size comparison of the Panasonic FZ2500 and Panasonic GX8. The Panasonic GX8 is clearly the smaller of the two cameras. Its body is 5 mm narrower, 24 mm shorter and 72 mm thinner than the Panasonic FZ2500.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.