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Scale Versus Gauge

One of the hardest concepts for new model railroaders to understand is the difference between the terms scale and gauge. The definitions of these two terms are very simple but how they are used or misused can be very confusing, especially to beginners. Even some experienced modellers seem to mix up these terms. Scale is the relationship between the model and the item it represents. For example, HO scale, which is usually expressed as a ratio 1:87 or as a fraction 1/87, one centimeter of the model is equated to 87 centimeter of the real item.

Gauge is the actual distance between the inside edge of the rails. What can be confusing is that this measurement can be equated to different widths of track depending on the scale you are modelling.

Most railways as we commonly see them at railway crossings are built to "Standard Gauge". This is a distance of “four feet eight and a half inches" or 56 1/2". This unusual width was officially accepted as the standard measurement for railway track in The Railway Act of 1875 in Canada and by a similar enactment in the United States. Prior to this time railways could not interchange their cars with each other, as their tracks were constructed in different gauges. Military troop movements and shipping of supplies during the US Civil War sharpened the need for standardization between railways and the creation of large railway networks.

Why 56 ½ inches? This measurement dates back to Roman Times when roads were built with ruts spaced at this width. That distance between ruts was required for chariots hauled by two horses. Design engineers do not like to give up on practices that work, even when they have no idea how old that practice has become.

Narrow Gauge, Broad Gauge, Standard Gauge?

What do these terms mean?

Not all real railroads were built to “Standard Gauge”. In the past some railroads were built to other widths or gauges. Some early British railways were originally constructed to gauges of five feet six inches (66") or even seven feet six inches (90"). These became known as "Broad Gauge Railways". While offering more stability because of their width, they cost more to build and maintain than the narrower “Standard Gauge” railways. Some were even built in Canada, but they were eventually narrowed to Standard Gauge so they could interchange traffic with other railways..

To minimize construction costs, many industrialists discovered that building their private railways to a smaller gauge or "Narrow Gauge" was less expensive than building a ‘standard’ railway. Since these railways did not connect with other railways, these stand-alone railroads did not have to interchange with major railway lines. Examples of this style of railroads are logging railways, carrying logs from the bush to the mill; or mining railways carrying ore to crushing plants.

Secondary railroads into mountainous country were also built to "Narrow Gauge" because the smaller locomotives and rolling stock were lighter and could be hauled up steeper grades and around tighter curves than their larger cousins. These features proved advantageous when building in narrow valleys between towering mountains. The Durango and Silverton is a famous example of such a railway that still operates, although primarily as a tourist railway.

How does all this relate to model railroading? In magazines and books relating to this hobby, you will see references to On30, HOn3, Gn15 and others. These terms refer to the Scale of the models (G = 1:22.5, O = 1:48, HO = 1: 87, or N = 1:160) followed by the letter n to designate that it is a narrow gauge model, and followed by a number indicating the width of the gauge. (3 = 3 scale feet between the rails, 30 = 30 inches, 15 = 15 inches, etc.)

Track built to represent HO scale Standard Gauge can be used to represent O scale 30-inch gauge, or G scale 15-inch gauge. Similar relationships exist for N scale Standard Gauge trackage.

Most modelers in this hobby choose to model in HO Scale (1:87), using Standard Gauge track to run their Standard Gauge HO Scale locomotives and rolling stock.

If you are still confused and wish to know more (not every one is interested in this knowledge) come and see us at The Credit Valley Railway Company Ltd. We have 'experts' who can help you learn more about this topic, and books to help you explore this and other related subjects in more detail.