Below you can see the front-view size comparison of the Fujifilm X-T20 and Olympus E-M10 III. The Fujifilm X-T20 is clearly the smaller of the two cameras. Its body is 4mm narrower, 1 mm shorter and 9 mm thinner than the Olympus E-M10 III.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.