The terms scale and gauge are two of the most confused terms in the model railroad hobby.

The SCALE proportion is expressed as a fraction of a real life-sized railroad. As an example, HO scale model train set is 1/87 the size of real life-sized railroads.

For model trains, track GAUGE is the width between the inside running edge of the rails. For toy trains, track gauge is the measurement from the center of the two outside rails.