Below you can see the front-view size comparison of the Fujifilm X-T3 and Pentax K-1 II. The Fujifilm X-T3 is clearly the smaller of the two cameras. Its body is 4mm narrower, 17 mm shorter and 27 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.