Below you can see the front view size comparison of Sony A6000 and Sony a5100. Sony a5100 is clearly the smaller of the two cameras. Its body is 10mm narrower, 4mm shorter and 9mm thinner than Sony A6000.
Sony A6000 vs Sony a5100 - Front View
Sony A6000 vs Sony a5100 - 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