Below you can see the front view size comparison of Pentax K-3 II and Canon 6D. Pentax K-3 II is 14mm narrower and 11mm shorter than Canon 6D but it is also 6mm thicker.
Pentax K-3 II vs Canon 6D - Front View
Pentax K-3 II vs Canon 6D - 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