Below you can see the front view size comparison of Fujifilm X-H1 and Fujifilm X-T3. Fujifilm X-T3 is clearly the smaller of the two cameras. Its body is 7mm narrower, 4mm shorter and 27mm thinner than Fujifilm X-H1.
Fujifilm X-H1 vs Fujifilm X-T3 - Front View
Fujifilm X-H1 vs Fujifilm X-T3 - Top View
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.
Camera Size Comparison
Select Two Cameras for Size Comparison