page_title: Scale model
section_title: Railways
hierarchical_section_title: Scale model / Examples / Railways
caption_attribution_description: A propane fired 1:8 scale live steam train running on the Finnish Railway Museum's miniature track. Photo by en:User:Janke 2006
context_page_description: A scale model is most generally a physical representation of an object that maintains accurate relationships between all important aspects of the model, although absolute values of the original properties need not be preserved. This enables it to demonstrate some behavior or property of the original object without examining the original object itself. The most familiar scale models represent the physical appearance of an object in miniature, but there are many other kinds.
  Scale models are used in many fields including engineering, architecture, film making, military command, salesmanship, and hobby model building. While each field may use a scale model for a different purpose, all scale models are based on the same principles and must meet the same general requirements to be functional. The detail requirements vary depending on the needs of the modeler.
  To be a true scale model, all relevant aspects must be accurately modeled, such as material properties, so the model's interaction with the outside world is reliably related to the original object's interaction with the real world.
context_section_description: Model trains come in a variety of scales, from 1:8 on the large end and 1:450 (T scale) on the small. Each scale has its own strengths and weaknesses, and fills a different niche in the hobby. The largest models are as much as 3 meters (9.8 ft) long, the smallest a few centimeters. The most popular size is HO scale (1:87) and second is N scale (1:160).
  Model railways originally used the term gauge, which refers to the distance between the rails, just as full-size railways do. Although model railways were also built to different gauges, "standard gauge" in 1:1 scale railroads is 4' 8.5". Therefore, a model railway reduces that standard to scale. An HO scale model railway would have track that is 1/87 of 4' 8.5", or about 0.65" from rail to rail. Now it is more typical to refer to the scale of the model, and the term scale has replaced "gauge" in most usages. This is despite considerable confusion between countries as to the definition of 0 scale and N scale.
  Considerable confusion often arises when referring to "scale" and "gauge", especially as the words are sometimes used interchangeably. The word "scale" refers to the proportional size of the model; the word "gauge" applies to the measurement between the inside faces of the rails. To highlight this difference, consider the various gauges used in HO scale; A gauge of 16.5 mm is used to represent the "standard gauge" of 4 ft 8 ¹⁄₂ in (1,435 mm) (HO scale), a gauge of 12 mm is used to represent 1,000 mm (3 ft 3 ³⁄₈ in) gauge (HOm) and the 3 ft 6 in (1,067 mm) gauge (HOn3-1/2) and a gauge of 9 mm is used to represent a prototype gauge of 2 ft (610 mm). It is completely incorrect to refer to the mainstream scales as "HO gauge", "N gauge" or "Z gauge"
  The most popular scale to go with a given gauge was often derived at by the following roundabout process. German artisans would take strips of metal of standard metric size to make things to blueprints whose dimensions were in inches: hence "4 mm to the foot" yields the 1:76.2 size of the "OO scale". This British scale is anomalously used on the standard HO/OO scale (16.5 mm gauge from 3.5 mm/foot scale) tracks, however, because early electric motors weren't available commercially in smaller sizes.
  There are three different standards for the "O" scale, each of which uses tracks of 32 mm for the standard gauge. The American version continues a dollhouse scale of 1:48. It is sometimes called "quarter-gauge", as in "one-quarter-inch to the foot". The British version continued the pattern of sub-contracting to Germans; so, at 7 mm to the foot, it works out to a scale of 1:43.5. Later, MOROP, the European authority of model railroad firms, declared that the "O" gauge (still 32 mm) must use the scale of 1:45. That is, in Europe the below-chassis dimensions must be slightly towards 4 feet 6 inches, to allow wheel/tyre/splasher clearance for smaller than realistic curved sections.
  "Live steam" railways, that people actually ride on, are built in many scales, such as 1-1/2", 1", and 3/4 inches to the foot. Common gauges are 7-1/2" (Western US) and 7-1/4" (Eastern US & rest of the world), 5", 4-3/4". Smaller live steam gauges do exist, but as the scale gets smaller, pulling power decreases. One of the smallest gauges on which a live steam engine can pull a passenger is the now almost defunct 2-1/2-inch gauge.
caption: A propane fired 1:8 scale live steam train running on the Finnish Railway Museum's miniature track.
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