Below you can see the front-view size comparison of the Olympus E-P3 and Pentax K-1 II. The Olympus E-P3 is clearly the smaller of the two cameras. Its body is 15mm narrower, 41 mm shorter and 52 mm thinner than the Pentax K-1 II.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.