The definitions of scale and gauge are as follows:
Scale is the ratio of the size of a model compared to the full-sized item. For O scale, the numbers are 1 and 48, so the ratio is 1:48 or 1/48, and the actual item is 48 times as large as the model.
Gauge is the distance between the inner edges of the track rails. On a standard gauge railroad in the United States, that distance is 4-feet 8-1/2 inches (56-1/2 inches). For American O gauge track (say Lionel), the gauge is 1.25 inches.
For O scale, the exact track gauge is (56-1/2 inches divided by 48) 1.1771 inches. In the United States, American O scale and O gauge track approximate this exact value using 1.25 inches instead. Proto-48 models are built to the exact track gauge. Three-rail O gauge models are built to a 1.25-inch track gauge which is equivalent to 5-feet at full scale.
MELGAR
