The difference between scale and gauge

[John Ashworth]

Interesting article here. They give N as 5/64" to 1' rather than the more commonly used 2 mm to 1'.

The difference between scale and gauge

September 1, 1:01 PM
Columbia Model Train Examiner
Matt Conrad

One of the most confusing things for newcomers to model railroading is the difference between "scale" and "gauge." They are often used interchangeably, but this usage is incorrect. The two terms are totally different concepts. Both terms have different meanings outside the realms of models and railroads, as well. This article will be restricted to modeling and railroading as far as that goes.

All about scale

Scale, to define it rather simply, is the proportion of a model to its prototype -- the real-world object the model represents. Scale applies to all models, not just trains. It's how a model builder keeps the model perfectly proportioned to the prototype. Scales can be expressed in two ways, proportionally or dimensionally.

Proportional scales are written as two numbers with a colon between them; i.e. 1:48 or 3:1. By convention, the model is placed to the left of the colon and the prototype to the right. So, the first example we gave above would be a model 48 times smaller than its prototype, while the second example should be a model three times bigger. Unfortunately, this convention is often violated out of ignorance, leading to more confusion. Generally, models are smaller than their prototypes, so if somebody screws up and writes the proportion backwards, just assume the smaller number (almost always a "1") is the model.

Dimensional format has essentially the same structure and convention as proportional format. The difference is that either an equals sign or the word "to" is used in place of the colon, and the numbers are measurements (usually in inches or milimeters). By doing some algebra we won't get into, you can determine that 1:48 works out to 0.25"=1' or one-quarter inch to the foot, and 3:1 works out to 3'=1' or one yard to the foot. Dimensional scales are usually expressed as some measurement to the foot, so the "to the foot" part is often dropped. Thus, our first example above could be called "quarter-inch scale."

Over the years, a number of standard scale proportions have developed. Standardizing on a few scales makes sense, especially with model trains. If John and Bill are both using the same scale, say the 1:48 we've been using as an example, then John's trains should be able to run on Bill's tracks and Bill's trains on John's tracks. War gamers also have standard scales (1:72 is common) so that the models on their game boards look right together. Even architectural models are usually built to one of several standard scales. In model railroading, the scale proportions have been given names in the form of letter codes to make them easier to remember and refer to. The table shows the standard model railroad scales in both proportional and dimensional notation, along with their letter codes or the name they are generally known by and their standard track gauge. Note that two-letter codes such as HO are pronounced as two separate letters ("aitch-oh"), not as a word ("ho").

All about gauge

Gauge, sometimes spelled "gage" in the railroad world, has nothing to do with scale. For railroaders, the term simply means the distance between the inside corners of the running rails. If you think about it, that dimension is pretty important. If there's too much variation in the gauge, the trains won't stay on the tracks! Therefore, some pretty tight standards have to apply to a railroad's gauge. These standards are usually dictated by some government agency to be sure that all railroads meet the standard. In the United States, that agency is the Federal Railroad Administration, or FRA. The standard railroad gauge in the United States, Canada, Mexico, the United Kingdom, and most of Europe and Asia is four feet eight and one-half inches, or 56.5". For our purposes, "standard gauge" means 56.5" gauge.

A secondary standard gauge of three feet quickly developed in the United States for railroads that needed to keep their construction costs low. Usually, "narrow gauge" was chosen for railroads in mountainous terrain because it required less digging and filling to carve out a roadbed for the track. Industrial railroads -- especially those operated by logging companies to haul lumber to their sawmills -- were another place narrow gauge was used extensively. A narrow-gauge railroad still operates near Cheraw, SC, hauling clay from a clay pit to the Palmetto Brick Company's brick factory.

In Southern Africa, most of the railroads were constructed to a track gauge of three and a half feet, or 42". This gauge standard became known as "Cape gauge" and is still in use. The railroads in New Zealand also use this gauge. In North America, Cape gauge was used for the now-abandoned railroad network in Newfoundland.

Finally, some railroads were built to a gauge measurement wider than the North American standard. These lines were known as "wide gauge" or "broad gauge" railroads. Prior to the War for Southern Independence, about half of the railroads in the South were built to five foot gauge, which became known as Southern standard gauge. These lines were converted to standard gauge during Reconstruction. There was even one railroad in the North, the Erie RR, that was originally built to six-foot gauge! The streetcar lines in most of Pennsylvania (mainly Philadelphia and Pittsburgh) and in New Orleans (which were funded by Philadelphia businessmen) were built to the odd gauge of 5' 2.25", sometimes called "Pennsylvania trolley gauge." Baltimore, MD also had an oddball gauge for its streetcars, measuring 5' 4.5".

In model railroading, gauge can get confusing. In the smaller scales, standard gauge is assumed when we discuss the scale by name -- HO scale modelers build 1:87 scale models of standard-gauge trains, for example. If someone is modeling narrow-gauge trains, the scale name nomenclature calls for a lower-case "n" to identify narrow gauge, and then the track gauge. A model of the Palmetto Brick Company in HO scale would be HOn3. There are very few modelers working in wide gauge, so no standard nomenclature applies to it. A logical wide gauge nomenclature would be something like HOw5.

Complicating matters these days is the fact that originally, trains were marketed by gauge rather than scale. In the early 20th century, manufacturers developed several partially-standardized track widths and approximately scaled their trains to match these gauges. The smallest of these was Gauge I (one), with Gauges II, III, and on successively larger. Lionel introduced a smaller Gauge 0 (zero), which was corrupted into O (oh) gauge. This was later used as the basis for HO gauge, or "half O." Manufacturing techniques were still rather crude, so scale was considered less important than operation. As a result, these early trains were much more toylike than today's models. This also meant that the standard scales that evolved didn't exactly match the track gauge. As a result, O gauge track actually scales out to about 5' gauge in 1:48 scale.

There's more confusion with what is today called "large scale." A German company called Lehman revived the all-but-obsolete Gauge I track in the 1970s for its "garden scale" trains, which were based on German meter-gauge prototypes. They standardized the track gauge at 45mm and the scale of their trains at 1:22.5. This created "G scale" which should, using the scale/gauge nomenclature, actually be called "Gnm." An American company adopted the 45mm gauge track, and started building trains that were compatible with Lehman's, but scaled so that the track represented standard gauge. These trains have become known as No.1 scale, or 1:24. Since a meter is close to three feet, many modelers began using G scale trains to represent North American three-foot gauge trains. Soon, modelers got picky about the gauge difference, The 45mm track gauge was kept, and the scale was adjusted to make it measure three scale feet. The resulting scale of 1:20.3 became know as F scale. Hence, we have three different scales that all use the same 45mm gauge track!

Standard Model Railroad Scales

Scale Name, Scale Proportion, Dimension that =1' , Standard Gauge
Z, 1:220, 3/64", 6.5mm
N, 1:160, 5/64", 9mm
TT, 1:120, 1/10", 12mm
HO, 1:87, 3.5mm, 16.5mm
OO, 1:76.2, 4mm, 16.5mm
S or 3/16", 1:64, 3/16", 22.4mm
O, 1:48, 1/4", 1.25"
No.1, 1:32, 3/8", 45mm
G, 1:22.5, 17/32", 2 33/64"
F, 1:20.3, 19/32", 2 25/32"
3/4", 1:16, 3/4", 3.5"
1", 1:12, 3/4", 4 3/4"
1.5", 1:8, 1.5", 7.5"

NB: That last bit is a beautifully laid out table in the original article, but we haven't discovered how to make tables work on our forum yet!

[Tom Macrery]

Very interesting. We knew the difference, but need reminding as we often use the terms (wrongly) as synonyms when discussing our models. Also the table of model gauges is instructive and includes many gauges I did not know about. For those who love the real world railroad gauges (ie not models) here is the website for a fully comprehensive list of the worlds railroad gauges (even the obsolete ones), from 1' lines in the UK and the USA, to Hitler's never-built 3 meter gauge.

http://parovoz.com/spravka/gauges-en.php or just Google 'Railroad Gauge Width', the first entry is the one you want.