There are many model railroad scales available today, and the Gatsme Model Railroad Club uses only one scale, HO (1:87).
The term “scale” should not be confused with “gauge“. “Scale” is the ratio of the model compared to the actual full sized prototype, where “gauge” is the distance between the two running rails of the track. For example, HO Scale is 1:87, where 1 modeled inch is equivalent to 87 real world inches.
The diagram below is a comparison of common railroad modeling scales used today.