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Houston Tinplate Operators Society - Lionel, Trains, Layouts: Scale & Gauge
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Scale & Gauge Overview

Have you ever been confused by the terms used for model or toy trains? Like the words "gauge" and "scale" for instance? How about the differences between model trains, toy trains, and prototype trains?

Modelers usually call the real world railroads "Prototypes" for two reasons: First, these railroads are original, one of a kinds; hence, the definition of the word prototype. Second, these real world railroads represent the "ideal" for the modeler, achieving this real world realism is the goal of many model railroad builders. However, to many hobbyists, the toy and model trains are the real trains.

The distinction between toy and model trains is one of proportion. So called, "Toy Trains", in which Lionel trains are categorized, do not necessarily remain true to all proportions or scale, whereas "Model Trains" are usually designed to be an exacting copy of the real item as possible.

Most railroad hobby clubs are centered around a specific gauge of track. HTOS runs O or O-27 gauge Lionel (or compatible) trains. These trains operate on tinplate style track (track with three rails) versus "O scale" track which usually have only two rails.


Gauge measures the space separating the two running rails. For all railroads real and model (except Lionel track) the gauge of the track is measured from the inside of one rail to the inside of the other rail. However, for Lionel style track, the measurement is taken from the centerline of the two outside rails on 3-rail track.

The spacing between the rails for toy and model trains has been customized, for the most part, to a few specific, standard spacings or gauges. Each one of these gauges has been given a letter code to indicate the width of the rail spacing. The table below shows a small selection of the letter gauges and the scales associated with them.


Scale, stated as a ratio, is the relationship between the model's dimensions, and the dimensions of the real world (prototype) item it represents. For example, if the prototype item is one foot long, and the model is one inch long, this is specified as 1/12th scale, or one inch to the foot. This ratio can be expressed in colon form; in this case 1:12 = 1/12th scale. This model is twelve times smaller than the prototype it represents.

A standard fifty foot boxcar in 1:12 scale would be fifty inches long, or 4 feet 2 inches. Of course, this scale is much too large for practical indoor use, so a much smaller scale is needed. In the table below, the scale associated with O gauge is 1:48 scale. With 12 inches per foot, and a size 48 times smaller, 12/48 = 0.25 or 1/4 of an inch to the foot. The same fifty foot boxcar in 1:48th scale now shrinks to only 12 1/2 inches long, a more manageable size for indoor operation.

A bit of history behind "O Gauge".

The O (or "oh") originally was a zero (0). The early model trains made by many of the toy makers used a variety of track widths. Definitions using gauge, rather than scale, was used more common in these early days with the four gauges for which standards were adopted being No. 0, No. 1, No. 2 and No. 3. Toy makers like Marklin, Ives, Lionel, Hafner, and other train makers popularized these larger or "Wide Scale" trains. These larger size trains lost favor partially because they were impractical to use inside the home. All of these larger track sizes were dropped during the start of World War I, mostly due to metal rationing and houses in general were becoming smaller. The Great Depression wiped out demand for these larger trains due to expense and by 1932, O Gauge became the standard by default. American Flyer ceased to make O Gauge trains in 1947 in favor of their own two-rail track design which became known as "S Scale".

Gauge/Scale Chart

The following table illustrates the most common gauges of model and toy trains currently in use in the United States. The chart shows only a small selection of the many recognized gauges of track. Other countries have additional gauges not seen in the United States. For more about the large variety of model railroad scales, see the Wiki article Model Railway Scales which is an excelent reference and expands on this simple chart below.

Gauge Rail Spacing Accepted
1.75 also used
1:24 also used
Standard (#1) 2.12554.01:26.59
O 1.2531.81:48

Gauge and Scale Relationships

Each letter gauge of model track is meant to represent the standard prototype track gauge. The scale associated with each letter gauge attempts to maintain the same proportion for the equipment as with the track.

Comparing the normal spacing of a prototype track (4 feet 8 1/2 inches), and the model rail gauges, exposes a small problem. For example, the chart shows O gauge uses a scale of 1:48 scale. Using that scale, 1/4 inch is equal to one foot on the prototype. With the normal O gauge track width of 1 1/4 inches wide (five quarter inches), this track would actually represent a measurement of five feet wide! In 1:48 scale, the actual distance should be approximately 1.1223958 inches, which is not a very convenient number to work with, so the gauge was rounded up to 1.25 (1 1/4) inches.

The reason for the inexact scale is buried in the history of O gauge, and was a compromise created for convenience of measuring, even though it's known to be incorrect. The O gauge tinplate track is actually closer to 1:43 scale. The Proto-48 scale exists to make O gauge and 1:48 scale technically accurate. The 1:48 scale is also a popular doll house scale size, as well as many other model toys, which makes a nice match in size for train layout use.

Altered Gauge and Scale

The prototype trains of today have a standard gauge of 4 feet 8 1/2 inches. Closer spacing between the rails (referred to as narrow gauge) is sometimes used, but not usually on mainline railroads. There are exceptions to this rule, such as the Denver and Rio Grande railroad that used three foot gauge mainline track. Most narrow gauge trains were used for short line and other special uses, such as mining, logging, or scenic tourist trains. A two or three foot gauge is common for these prototype railroads.

Some modelers may decide to alter the actual scale for a given track gauge in order to add an interesting operation detail to their layout. For instance, fabricating a narrow gauge mining train in HO scale, could be accomplished by laying N gauge track, then changing only the trucks on the HO equipment to operate on that track gauge. The designation for this track gauge is called "HOn2.5". The layout and train scale is HO (1:87.1), and the track gauge (n2.5) represents a narrow gauge 2 1/2 foot wide track. When a modeler wishes to create this narrow gauge railroad, track might be hand laid or one of the standard off the shelf track gauges could be utilized if appropiate. It just so happens that the HOn2.5 gauge matches the regular N gauge width. An appropriate ratio between the size of the equipment and the width of the track exists with this arrangement.

About O-27 Track

Lionel uses two track systems, O-27 and O. The O-27 track is the same width as regular O gauge track. The difference is the rail height, tie size, section length, and metal thickness, making the track smaller and lighter than the typical O gauge track. This was done to reduce the cost of making the track. Regular O gauge track has a rail height of 11/16 inches and O-27 track is 7/16 inch tall. The rolling stock and locomotives that Lionel catalogued to run on O-27 track generally are smaller and lighter as well. The actual scale is smaller for the equipment, too, but the difference is usually ignored.

Trackwise, the main difference between O and O-27 is the diameter of the circle created by standard curved sections. The 27 in the name refers to the circle size created by eight pieces of track. Lionel O-27 track will make a circle 27 inches in diameter. Eight pieces of Lionel O gauge track, on the other hand, make a 31 inch diameter circle. The curves of the O-27 track are smaller, so longer equipment overhangs the track curve more and may not clear the housings on the turnouts (switches) which are also smaller. O-27 style track is also available in a variety of circle diameters besides 27 inches.

It is possible to mix O and O-27 track with special reduction pins and shimming the height of the track junction. However, most regular O equipment is usually too large to operate smoothly on the much smaller curves. This can become particularly a problem in the switch machine bodies which can snag the larger trains and have clearance problems.

Toy Train Scales

Now comes the really confusing part. A bit of liberty is sometimes taken with the scale, especially with toy trains, in order to make everything appear to be in proportion or to make the train run better. In fact the standard fifty foot boxcar with Lionel trains is closer to 10 inches in length rather than the 12 1/2 inches called for in 1:48 scale. The actual size may be even smaller for O-27 equipment. A given piece may be closer to 1/64 scale or, at times, to 1/43 scale. These modifications mean the the trains are no longer 100% "true" to scale. The smaller O-27 pieces still have the same size coupler and wheels as O gauge, allowing compatibility with regular O gauge equipment. This further distorts the scale of an individual piece.

Trackside equipment may be grossly out of scale. Historically, miniature motors, lights, and electronics did not exist back when most of this equipment was designed. The larger operating parts necessitated larger equipment. The size of the accessories and other track side equipment was also selected to give a piece a better "play" value for small hands. It made operation easier and was more rugged, as it was designed to be a toy. Specific model engines also may have been changed by removing details or making them shorter than true scale to allow better operation. In some cases, entire features (trucks, drivers, steps, ect.) may have been omitted, to make the piece more durable.

The inaccuracy in scale is why some "Model" railroaders prefer to separate themselves from so called "Toy" trains. Most model railroads are closer to scale, at least within the specifications outlined by a specific letter gauge. Closer examination of the scale chart above will reveal that some scales used are not quite exact. This is mainly for convenience, strength and for historical reasons.

As railroad owners running Lionel compatable equipment, HTOS takes this inaccuracy of scale in stride. Lionel and other train manufacturers now make more scale items than ever before. For the purist, there are ready to run pieces of equipment made by several companies in true-to-scale proportions. Most purists of course object to the third center rail, but then, they're not running Lionel style equipment. As can be pointed out, some prototype electric trains do use a third rail, often times outside the running rails, but can also be found inside between the running rails. Railroad hobbyists running O gauge "toy" trains may place their trains in a more scale setting. This type of semi-scale operation is sometimes referred to as "Hi-Rail."


The term "Hi-Rail" means different things to different people. Some use the term to refer to toy trains in general. Others reserve the term for toy trains used in a scale setting with scale trackside equipment and scenery. Sometimes Lionel trains are refered to as "Hi-Rail", because the scale of the track is not "true." Prototype railroad mainline track is about 5 inches tall from the tie to the top of the railhead. In comparison, the height of regular O gauge Lionel track rail is 1/4 inch tall. In 1:48 scale, this would make the rail itself about one foot tall and the wood ties would be nearly two feet wide and over one foot tall piece of wood. The flange on the wheel of prototype railroads is very small, somewhere around 1/2 inch. On Lionel type equipment, the wheel flange is about 1/8 inch, using the 1:48 scale, this would be the equivalent of a 6 inch flange. With these overly large sizes one can see why Lionel trains are sometimes refered to as Hi-Rail.

Also trains run in the Hi-Rail world are not necessarily 100% to scale; sometimes a given piece may be closer to 1/64 scale and at other times closer to 1/43 scale. Hi-rail trains are to be judged more on their operability, durability, and (we think) "HIGH" level of enjoyment!

When speaking of O gauge trains, the name "Lionel" springs to mind, bringing back memories of Christmas Trees, Coca-Cola, and lots of heavy-duty fun. Surprising to some, Lionel is not, and never has been, alone in the world of O gauge trains. In the last few years there has been a strong surge in the production of O gauge trains.

In the field of O gauge only production, K-line Corporation (now owned by Lionel) produces a large number of quality O and O-27 size trains. Mike's Train House (MTH), also produces O gauge products and is quickly becoming highly recognized for their great attention to detail in full scale trains. Sadly, it appears that the company that was starting to re-issue MARX tinplate trains has gone out of business.

There are also manufacturers that produce both O gauge 3-rail and O scale 2-rail versions of the same equipment. These include Weaver, Williams (now owned by Bachmann), InterMountain, and the predominately brass manufacturer, 3rd Rail. If you want to combine the fun and action of 3-rail operation with the beauty of pure scale, these pieces are for you.

HTOS and Scale

HTOS takes scale in stride. Club members enjoy running Lionel and compatible equipment for the fun and love of the hobby. If some things are out of scale, who notices with all those wonderful trains rolling down the tracks? The club's portable layout was completed with regular Lionel tubular track. Regular Lionel trackside equipment pieces, and Plasticville or scratch built buildings were used to create layout scenery and aren't necessarily true to scale. The portable layout was intentionally designed to be similar to the style a novice might create, or as might have been done by Lionel operators.

The permanent layout mostly employs track manufactured by the Gargraves Trackage. Turnouts are made by Curtis and Gargraves. The rail shape is closer to prototype, has real wooden ties and is more to scale. The curves are broader, 48 inches to over 96 inches in diameter, and the track layout style is similar to prototype lines. Prototype signals and trackside equipment have also been used. The permentent layout was constructed with a greater regard to scale. However, it still might qualify as a "Hi-Rail" layout to some.

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