• The gauge of a layout is the distance between the rails of a single track. The stability of this dimension is critical. Any discrepancy in the rails will cause derailments because the wheels of the train are fixed and cannot be adjusted.
The importance of gauge size is more complex than just a dimension.

In part the hobby of model railroading is very successful mainly because the components are competitively priced. The manufacturers have therefore been forced into dimensional consistency and stability because the large manufacturers make model trains rolling stock and all accessories for all gauge sizes. Thankfully this reduces the cost for us and increases choice.

• Uniformity is essential because if it was absent each manufacturer would have their own unique gauge's and scales, prices would rocket and availability would inevitably suffer.
The easiest way to explain the two terms; gauge and scale is to talk about them both at the same time. Remember though that gauge is the track dimension and scale is the train size description.
Large-scale trains.

Large model layouts all comprise of Gauge 1 track. This track has 45 mm between rails. If it was all as easy, many of the large scale installations are outside in the yard or in a barn.

• Many of these trains are used by aficionados who run their systems outdoors. The locomotives look great, pulling their cars through flower and herb gardens.

The locomotives are quit big. Think of a full scale 50-foot-long locomotive: In a 1:29 scale (1 inch represents 29 feet), the model train would be approximately 20¾ inches long!

"O" is he most popular gauge. The gauge for "O" is 1 ¼ inches; the scale is 1:48. That same 50-foot-locomotive, in this model scale, is about 12 ½ inches long.

• S-gauge Just a bit smaller than "O" gauge as are the train models. This size has tracks with a gauge of 7/8 inches and a scale of 1:64. Our prototype 50-foot locomotive is only 9 and 3/8 inches long in this
Small but Very….Very popular. Those above the largest of the trains. So how small are the small ones then?

• There's the HO gauge. HO literally stands for "half of O". This class of trains is built to be exactly one half the size of "O" gauge models. When compared to the full-size trains, the HO has a scale of 1:87. That makes our 50-foot, life-size locomotive prototype just 7 inches long in this scale.
This may appear very small to you; in fact extremely small, but the HO models are an ideal size for building a great layout where space is an issue. These locomotives are large enough to display detail, and they really are quite easy to work with.

• HO is the most popular of all model railroad gauges and scales. More than two-thirds of modellers rank it as their favourite size!
But we go even smaller than that when we view the "N" gauge. This model, with a scale of 1:160, has a gauge of 9 mm between the rails. It's preferred by hobbyists who don't have as much room as they'd like for their layouts. There are some massive N gauge layouts to be seen and the some very wide range of scenery and accessories available.

• There are other model train scales and track gauges but they are either massive or very small. The extreme top and bottom of the size range represent a very small sector in the Railroad modellers scope so we will not go into detail right now.