Below you can see the front-view size comparison of the Fujifilm X-T1 and Fujifilm X-T3. The Fujifilm X-T1 is clearly the smaller of the two cameras. Its body is 4mm narrower, 3 mm shorter and 12 mm thinner than the Fujifilm X-T3.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.