Below you can see the front-view size comparison of the Ricoh GXR S10 24-72mm and Pentax K-S1. The Ricoh GXR S10 24-72mm is clearly the smaller of the two cameras. Its body is 7mm narrower, 23 mm shorter and 26 mm thinner than the Pentax K-S1.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.