Beginner's Guide to Model Railroading

What Does Gauge Mean?

Definition of Gauge
The width of model railroading track as measured between the inside rails in millimeters or inches.

Be careful here. Scale represents the size of a model train to its prototype; the term gauge, however, refers to track width and is the distance measured between the inside rails in millimeters or inches. In America, we use inches (the English system); all other countries use the Metric system.

For example, HO-scale model trains operate on 0.650” (16.4mm) gauge track; N-scale model trains operate on 0.354” (9mm) gauge track. Simply refer to HO-gauge tracks or N-gauge tracks.

Just remember that scale refers to the size of the train and gauge refers to the width of the track. Some people refer to track as HO-scale or S-scale or O-scale. This is incorrect. Tracks are always referred to by their gauge.

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More On Gauge

The confusion between scale and gauge began with the AC Gilbert Company and its American Flyer (AF) brand of trains. AF produced 027 "gauge" trains before "scale" was applied to the model railroading industry. Because of the popularity of the AF brand, gauge became interchangeable with the size (or scale) of model train sets. Later model train manufacturers applied the term scale to differentiate between the various sizes of trains (O-scale, HO-scale, N-scale, etc.), and reserved gauge for designating track widths. Thus, an entire generation of model railroaders thought of scale and gauge as representing the same concept (HO-scale and HO-gauge meant the same thing). Today, scale refers to locomotives and rolling stock, while gauge refers to model railroading track widths.