What LEGO set has the biggest box? I know the 2017 LEGO Star Wars Millennium Falcon is the biggest set in terms of piece count, but what is the biggest box a regular set ever came in?

By regular set I mean produced for the mass markets, and not something like The ultimate battle for Chima (just an example, not saying that it is the biggest box).
As far as regular sets go (ie. no furniture or big-boxes like that Chima combo), the current UCS Millennium Falcon does appear to be the largest box by total volume.

75192-1 Millennium Falcon - UCS (2nd edition)

54 x 45 x 39 cm = 94770 cm3

54 x 45 cm = 2430 cm2



The original UCS Millennium Falcon box was actually larger in 2 directions however, though the total volume is smaller.

10179-1 Millennium Falcon - UCS

64.39 x 47.63 x 19.69 cm = 60387.176333 cm3

64.39 x 47.63 cm = 3066.8957 cm2



There appear to be a number of sets that are larger in at-least one direction, see this answer for the longest one identified so-far.