Below you can see the front view size comparison of Panasonic GX8 and Pentax KP. Panasonic GX8 is 23mm shorter and 13mm thinner than Pentax KP but it is also 1mm wider.
Panasonic GX8 vs Pentax KP - Front View
Panasonic GX8 vs Pentax KP - 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