Scales and Gauges

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When describing live steams models and railroads the terms "scale" and "gauge" (or both) are used to describe the size of the equipment. The two terms can be defined as follows:

  • Scale (ratio) - The scale ratio of a model represents the ratio of a dimension of the model to the same feature of the original. Examples include a 3-dimensional scale model of a locomotive or the scale drawings of the elevations or plans of a locomotive. In such cases the scale is dimensionless and exact throughout the model or drawing.
  • Track gauge - In rail transport, track gauge is the spacing of the rails on a railway track and is measured between the inner faces of the load-bearing rails.
Correct way to measure gauge

The scale can be expressed in four ways:

  • in words ("one inch to one foot")
  • as a ratio (1:8 scale)
  • as a fraction (1/8 scale)
  • as a graphical (bar) scale

See also IBLS Track Standard.

Common Gauge Names

Mike Massee offered the following names of the various gauges used in Live Steam.

  • 45 mm (1.772 inch) gauge - G-scale (Garden Scales)
  • 2.5 inch, 3.5 inch, 4-3/4 inch and 5 inch gauge - Small Scales Live Steam
  • 7.25 inch or 7.5 inch gauge - Live Steam
  • 9 inch through 22 inch gauge - Grand Scales Live Steam


  • 9 inch gauge is now very rare. One major railroad still exists (Mesa Grande Western Railroad) 1/4 inch scale of 36 inch gauge (i.e. 3 inch scale). There was a major 9-7/16 inch gauge railroad - the Centerville and Southwestern Railroad, which existed in the 1950s. Unlike the MGW it was standard gauge prototypes.
  • 12 inch gauge commercial use was popularized by Herb Ottaway. Only one major 12 inch gauge club remaining in the states, and one 12 inch gauge commercial operation (Folsom Valley Railway, with a narrow-gauged Ottaway formerly owned by Erich Thompsen of the Redwood Valley Railway) and more private 12 inch gauge tracks. Miniature Train Company also made 12 inch gauge park trains.
  • 15 inch gauge is the most common in grand scales. The so called "Minimum Gauge" coined by Arthur Heywood as also having utility on a practical level beyond excursions.
  • 16 inch gauge - mostly used by the Miniature Train Company park trains - the MTC-16 series.
  • 18 inch gauge is both a common US commercial park train gauge and early British industrial gauge.
  • There is one private 19 inch gauge railway, the Swanton Pacific, with all of the locomotives from the 1915 Panama Pacific Exposition built by Louis MacDermot.
  • San Francisco Zoo Railroad is 22 inch gauge with a rare Cagney "E" class locomotive currently being restored by Hillcrest Shops.
  • When you get to 23 and 23.5 inch gauge you're getting into full size that was intentionally brought below 24 inch gauge to avoid FRA oversight. Of course there are also "full scale" 15 inch and 18 inch gauge industrial and estate railway engines in Britain (and those few exported abroad) as mentioned above, so there is some overlap at the larger gauges of full size and scale models.
  • General note - scales on gauges vary widely. You could almost consider 3-3/4 inch scale equipment on 7.5 inch gauge as being 'grand scales' as they are much larger than many 12 inch gauge engines. I tend to separate by gauge and not scale, because there is a very large difference in participation and frequency of 7.x inch users vs. anything larger in gauge. (or anything smaller, for that matter) which is the whole point of 7.5 inch currently just being "Live Steam"...they have the numbers to be the vast majority at the moment, so they can have the generic title and everyone else can have a prefix.

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