FAQ:Whats the difference between scale and guage?

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SCALE describes the size of a model compared to the real thing. For example, "HO" scale is 1:87 (1 to 87; 1/87 of life size; you'd need 87 of an item strung end-to-end to be the same length as the real thing). "O" scale is 1:48 or a quarter inch to the foot. Therefore, one inch in O scale would represent 4 feet (or 48 inches) in the real world. For example, a door 7 feet high would be 7/4" high in a model. (Or in metric, about 2.1 cm to the metre.)

GAUGE refers to the distance between the rails. The rails on life-sized track are 4' 8-1/2" (56.5") inches apart (measuring the inside edges). Narrow gauge track has the rails closer than that, such as 36", 24" or in Europe, 1m; many variations of narrow gauge exist.

In the model world, "O" Scale is 1:48. The Gauge for most "O" track is 1.688" between the rails. "On30" trains (On30 - that's "Oh" scale n="narrow gauge" 30 inches between the rails) are normal 1:48 Scale, but run on rails that are closer together than regular "O" gauge track. On30 track just happens to have rails spaced the same distance apart as the track most HO scale trains run on! So modelers can use regular HO gauge track, but run narrow gauge O Scale trains on it.