The distinction of O scale vs O gauge can be confusing for some people, especially newcomers to model railroading. Some people can get uptight about the difference, so here’s how to distinguish the two so you can avoid offending someone.
O scale vs O gauge: More than the track
Strictly speaking, in model railroading, scale refers to the ratio of the size of the model in relation to the real thing. An O scale train is 1:48 the size of the real thing.
Gauge in model railroading refers to the width of the track. O gauge track is 1.25 inches between the rails.
There’s a distinction in O scale/O gauge that doesn’t happen with other scales, however. Generally speaking, when someone refers to O scale, they are referring to 1:48 scale models running on 2-rail track. O gauge trains generally mean trains that may or may not be true 1:48 scale models running on 3-rail track.
When Myron Biggar bought the magazine O Scale Railroading in the 1980s and decided to expand its coverage to include Lionel trains, he changed the name to O Gauge Railroading.
Why the number of rails matters
Traditional O gauge trains, produced by Lionel and others, operated on three rails to make wiring simpler on intricate layouts. A Lionel layout can loop back on itself with no electrical issues without doing anything special. Lionel varied the size of its trains to hit various price points. Scale, accuracy and realism were always secondary concerns.
Serious model railroaders who wanted realism above all else adopted O scale, especially before HO scale emerged. Today, 2-rail O scale is far less common than it once was, but the market segment still exists.
In the 1990s, Lionel and its competitor MTH started paying more attention to realism and marketing trains that were proper 1:48 scale, although they still operated on three rails. This accelerated a trend toward more realistic 3-rail model railroading. Typically, this type of modeling is called hi-rail to distinguish it from 2-rail O scale.
Some hobbyists have attempted to create a distinction in between hi-rail and 2-rail O scale, using scale wheelsets, scale couplers and sometimes even handlaying track, but still using three rails. They call this 3-rail scale.