The 3 series has less total passenger volume than a Civic (96 cu. ft vs 98), less trunk volume (13 cu ft. vs 15), less front legroom (42 vs 42.3), less front shoulder room (55.1 vs 57), and less rear legroom (35.1 vs 37.4). It has marginally more headroom, and that’s about it.
It pales compared to the Accord in space.