What scale is this train set? I mean 1:24, 1:22.5, etc.

Depends what the railway is representing. It matters, for example, whether you are in the US or Europe.
I recommend that you contact the company to get an unambiguous answer
Contact New Bright
Further reading on G-gauge can be found here
scale Wikipedia the free encyclopedia from which you will understand why it is not straight forward to answer your question with information available. In the US, the article says,
" 'Gauge One' scaled at 1:32 (3/8" to the foot) used to model standard gauge trains of 4 ft 8 1?2 in (1,435 mm) standard gauge gauge."
hope this helps (a bit)