Below you can see the front-view size comparison of the Olympus E-PL6 and Pentax K-S1. The Olympus E-PL6 is clearly the smaller of the two cameras. Its body is 10mm narrower, 29 mm shorter and 32 mm thinner than the Pentax K-S1.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.