Model “Scale” means the proportion that a representation of an object bears to the object itself. In model railroading, the term “scale” is often used interchangeably with (and often confused for) the term “gauge.” However, gauge is the distance between the track rails. In full scale railroading, the Standard Gauge used in most of the world is 4 feet 8 ½ inches. Some of the more common US model railroad scales are listed below.
G scale is the popular “Garden” size of model train. There are a few different scales used for this size. The scale in the United States is generally 1:20.3 although 1:24 is also used. The theoretical gauge is 1.791”, but in practice it is 1.77” or 1.75”, which is approximately equivalent to 45mm.
O scale is 1/48 of full size, which translates to ¼ inch to the foot in scale. Lionel made this scale popular in the past. The theoretical gauge is 1.177”. In practice, the Lionel model gauge is 1.25” (which would make a 5’ gauge). There are several current manufacturers, including Lionel, Mike’s Train House (MTH), Williams and others. This scale also has a category called “Proto 48” which models closer to the 1.177” gauge and has more exacting details.
S scale is 1/64 of full size, which translates to 3/16 inch to the foot. The theoretical gauge is 0.8828”, while in practice it is 0.885 (7/8”). American Flyer popularized this scale from 1945 to the early 1960’s. Current manufacturers include American Flyer division of Lionel, and American Models.
HO Scale is not exactly “Half O” scale but is instead 1:87.1 scale, which is 3.5mm to the foot. The gauge in theory would be 0.6487”, but in practice is 0.65” or approximately 16.5mm. This is probably the most popular scale in American model railroading, a fact which is reflected in both the number of manufacturers and the lower prices for the products.
N Scale is growing in popularity because the smaller size gives more railroad in less space, and smaller prices. Modern manufacturing techniques result in very high quality and detail in this scale. The accepted scale is 1:160, or about 75/1000ths of an inch to the foot. The gauge is 9mm.
Z Scale is obviously rather small, being at a scale of 1:220, which is 55/1000ths of an inch to the foot. The gauge is 0.256”, or about ¼ inch (6.5mm). The German company Märklin has promoted this scale. The small size does not come cheaply, however.
Surveys regarding the percentage of modelers in each scale show that HO leads the pack at around 78%, N is next most popular at 28%, O (3-rail) and Large Scale or G are tied at around 11%, O (2 Rail) is about 5%, S is 3%, Z is 2%, and all others total about 6%. If you add these up, that comes to well over 100%, meaning many people model in more than one scale. Many other scales exist, including 1 (1:12), I (1:32) OO (1:76) and TT (1:120).
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