Below you can see the front view size comparison of Sony A6400 and Samsung NX30. Sony A6400 is 7mm narrower and 29mm shorter than Samsung NX30 but it is also 2mm thicker.
Sony A6400 vs Samsung NX30 - Front View 
Sony A6400 vs Samsung NX30 - 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