You know, I honestly don't even remember, completely. But it was based in part (large part) on the size of the Falcon, related to its docking bay.
Scrutinizing the trench on my model, and factoring a lot of imagination, I imagined the Falcon would be about 1mm or 2mm.
Of course, this is all for fun, and subject to HUGE variability.
On the original model, the largest trench lights were between 1mm or 2mm.
I suppose we could re-think this...
The Falcon was sucked into one of the smaller bays, right? So if the largest lights on the model were 2mm, how big would the largest bays be?
The Falcon's bay (the set) was what - maybe 150 feet wide? So perhaps the largest bays were closer to 300 feet.
Which would put a millimeter closer to 100 to 200 feet.
Or, alternatively, if I am generously over-estimating the size of the Falcon juxtaposed to my model - perhaps doubling its size - then a millimeter would (again) be about 120 feet.
Again, highly subject to guess work, and all for fun. But it
is fun!