00 scale is 1:76 (4mm = 1 foot). So to make Trainz routes appear to be 1:76 scale models, the artefacts to create the simulation must be 76 times "real" size. I made my models - table, chair, cupboards, etc. - using real sizes in GMax, then made them 76 times bigger by scaling them up by 7600%.
0 scale in the UK is 1:43. Artefacts to simulate an 0 scale layout in Trainz must thus be 43 times larger, a factor of 4300%.
G scale being 1:22, the artefacts to create the illusion nust be 22 times larger than real, a factor of 2200%. The larger the scale, the smaller the artefacts to create the illusion.
So, a table 2' 6" high in real life would, for 00 scale, be 55' high, or 16.8 metres (as used by Trainz).
For N scale experiments (1:148 UK) I used a scaling factor of 14800%.
A Trainz baseboard, 720 x 720 metres, represents 9.47 x 9.47 metres, slightly under 31' x 31' in 00. On this basis, when creating a 00 virtual model railway I use an approximate scale of 2 metres Trainz = 1 inch imperial. Each 10m x 10m square thus represents 2.5 x 2.5 inches. This can be checked using the Trainz ruler spline - and is near enough for me without too many other calculations!
Baseboards for all other scales can be calculated and measured similarly. I personally use each 10m x 10m square to represent 5 inches in N scale, and a baseboard measures around 15 feet square. One baseboard for a garden would give a plot 32.7 metres square to cultivate.
I am aware that HO scale, as used elsewhere, is slightly different, but if OO/HO is good enough for Peco, it's good enough for me. In any case, artefacts come in diffent sizes.
Finally, whatever scale is imagined, you get no more length of railway along one baseboard. However, if like me you want to ensure that you can re-rail any derailed Trainz on the layout by keeping all tracks within arm's reach, about 2'6", you get twice the width to play with in N scale - and much less in 0. In the garden, it wouldn't matter - you can just walk round and pull up a few weeds at the same time.
Ray