Are you thinking in
Scale or Gauge
When you're asked what scale do you run, do you answer, "G-gauge." What G-gauge?
The problem with the term G-gauge is that, in reality there is no such thing! It refers to the Number 1 gauge track. The oldest existing gauge track in existence.
Originally "G-gauge" meant LGB.
LGB selected Number 1 gauge as the track width, which is 45mm, for their "narrow gauge" Garden Trains. Number 1 gauge track was around before the turn of the century and readily available.
They then selected European O Scale (1:45) and doubled the scale of the locomotives and rolling stock. This made the scale 1:22.5. In doing so they now had a fairly realistic representation of a one meter narrow gauge in Europe. For years they were the standard in "narrow gauge" garden trains.
Therefore, LGB is in 1:22.5 SCALE as are Bachmann.
Aristo-Craft  and USA Trains are in 1:29 SCALE, Aster and Row & Company are in 1:32 SCALE. They build standard gauge locomotives and rolling stock. There are also a few specialty manufactures that make a 1:20.3 SCALE, a true three-foot narrow gauge, rolling stock.
But, they all use the same 45mm track or Number 1 gauge ("G-gauge")!
So, in what Scale do need your Scale Card and Scale Rule?