Gauge is the measure of the distance between the rails on a real or model railroad track. Standard gauge is a generally accepted rail width used in many different real or model train tracks. The purpose of a standard gauge is to allow the same engines and cars to run on multiple lines.
Real-world standard gauge is 1,435 millimeters (4 ft 8 1/2 in). Standardization makes it possible to create long-distance high-speed lines that run between different countries or states. The first standard gauge railways were created in Britain during the 1860's. Parts and cars from these lines were imported to the United States, so that American train lines, too, ran on standard gauge.
Why are standard gauge railways 4 feet 8 1/2 inches wide? The reasons are not clear. Some say that the width represents the width of a Roman chariot, while others suggest that it may be the usual width of a horse-drawn carriage. Whatever the reasons, the gauge stuck: today, about 55% of train lines around the world are built to standard gauge.
Model Train Standards
Most model train scales are also built to conform to a common gauge that at least approximates standard gauge.
G gauge trains share a common gauge but are sized differently to make that gauge appear either standard or narrow. These very large model trains are specifically designed to be used in a garden setting.
HO trains, now among the most popular available, have a track gauge of 16.5 mm and a scale of 1:87. The S gauge, at a scale of 1:64, is slightly smaller than HO. Most O scale rails are spaced 1 1/4 inches or 32 mm apart, though the gauge may vary from country to country.
Trains running on tracks wider or more narrow than 56.5" are said to be broad or narrow gauge respectively. Narrow gauge trains are far more common. These too, are modeled in almost every scale. For model trains, a narrow gauge is indicated by the letter "n" after the scale, followed by a number which indicates the gauge. "On3" would be 3' narrow gauge in O scale for example.
Lionel Standard Gauge
With model trains, the standard gauge can also refer to a size of model trains produced by Joshua Lionel Cowen (Lionel) from 1906 to 1937. These trains were slightly larger than the O scale trains which superseded them with an actual track gauge of 2 1/8". Lionel began producing O scale trains, with a gauge of 1 1/4", in 1915.
Once the Lionel standard gauge train was introduced to the market, it quickly caught on. In a short time, it was outselling the competitors. Smaller and easier to produce than other similar model trains on the market, Lionel's standard gauge became popular with other manufacturers. As the trains become more readily available, they became increasingly popular.
In 1937, the Lionel company began making more accurate scale models of real trains—and the once-popular standard gauge was discontinued. Today, these original standard gauge trains are highly collectible and can bring big money in good condition. Reproductions have also been made by several companies.