Below you can see the front-view size comparison of the Nikon 1 J3 and Olympus PEN-F. The Nikon 1 J3 is clearly the smaller of the two cameras. Its body is 24mm narrower, 11 mm shorter and 8 mm thinner than the Olympus PEN-F.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.