If you think they are all the same size, you have not looked very far.
The main variation in tracks is the GAUGE. (Note the spelling, it is not GUAGE as you will sometimes see.) Gauge is always the measurement between the inner faces of the rails. For mainline US tracks this is 56.5 inches. If you are talking about logging tracks, 36 inchs was the general standard in the US. There are many other gauges but I guess that 56.5 inches is the one you want
Auran track height standard, top of the rail to ground level, is 300mm
Peter