Below you can see the front-view size comparison of the Pentax K-S2 and Olympus E-M10 III. The Olympus E-M10 III is clearly the smaller of the two cameras. Its body is 1 mm narrower, 7 mm shorter and 23 mm thinner than the Pentax K-S2.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.