O Scale vs. O Gauge - What's The Difference?

One of the more confusing concepts for beginning hobbyists is understanding the differences between O Scale and O Gauge and how these differences affect our modeling choices. Adding to the confusion is the fact that many hobbyists, and even some manufacturers, use the terms interchangeably when they are, in fact, distinct and separate concepts.

O Gauge

In railroad terms, "gauge" refers to the distance between rails on the track. For example, the "standard gauge" (not to be confused with Lionel "Standard Gauge trains of the 1910's - 1930's ---That's another post!) used by the vast majority of North American and British railways is 4' 8 1/2". There are, however, other track gauges in use such as 3' gauge, Meter Gauge, 30" Gauge, 5' Gauge and more. In model railroad terms O Gauge (technically it should be 0 or "zero gauge", but that's another blog post!) refers to any train running on track that is 1 1/4" between the outermost rails.

A variety of different toy trains that use O Gauge track.

In the photo to the left we see a collection of toy and model trains that all use O Gauge, 1 1/4" track. Obviously, these trains differ in size, detail and their manner of reflecting reality, but they all operate on O Gauge track nevertheless. So as modelers, simply knowing that a train is O Gauge is not enough information to determine how effectively it will operate with other trains or in our overall modeling and operating scheme.

We also must consider whether the model is built to be operated on 3-rail or 2-rail track. 2-rail locomotives use a different method of electrical pickup than 3-rail locomotives and the two are not interchangeable. For rolling stock there are differences in wheel types, wheel flanges, and coupler types that make 2-rail and 3-rail O Gauge trains mostly incompatible. Why do we use three rails in the first place? Again, that is a topic for another article! In the mean time, just accept that we do.

O Scale

In modeling terms, "scale" refers to the relative proportion of the model to its real-life counterpart, or "prototype" as we say in the model universe. HO Scale models, for example, are built to a proportion of 1/87 actual size.  S Scale models are 1/64 actual size. O Scale models are built to a proportion of 1/48 actual size (or sometimes 1/43 actual size but again, that is a topic for another article!).

Another way of thinking about scale is to determine what measurement is equal to a "scale foot". This is similar to the scale of a map with such measurements as 1" to the mile or 1" to 100 miles. O Scale is generally thought of as 1/4" = 1 actual foot. However, we see quickly that by that scale our 1 1/4" track would be 5' gauge, not 4' 8 1/2". Frankly, most modelers ignore this discrepancy in a favor of the easy math of 1" = 4'.

When "Scale" Is Not Scale

Four different O Gauge boxcars. Each is "scale", but only one is O Scale.

O Scale is a wonderful proportion to work with for modeling. Details are easy to see and simple to construct. Trains are large and easy for kids of all ages to handle - even those who wear trifocals. The disadvantage, however, is that trains built to true 1/48 scale require a great deal of real estate to turn around realistically. Since very few of us have room for layouts large enough to accommodate track curves in excess of 12' in diameter, manufacturers have devised methods of making these trains capable of navigating tighter curves. One of these methods is the use of different "scales" with O gauge track.



In the photo above we see four different O gauge boxcars. Each of which is a "scale" model, but only one is proportioned to O scale. The New York Central car in the back left was made by Auburn Models in the early 1950's and was proportioned to be a true 1/48 O scale model of a common 40' boxcar. The yellow Chessie System car to its right is also more or less a scale model of a 40' boxcar but it is proportioned to a slightly smaller scale, roughly 1/50. This car, made by Lionel in the 1970's, is identical in size to the Lionel 6464 series cars of the 1950's to the end of Postwar production in 1969. Many hobbyists refer to this size - slightly smaller than true O scale - as "traditional size".

On the near track, the Southern Pacific car in the front right is a K-Line car based on 1950's to 1970's era Marx tooling. These cars, like most Marx 8-wheel cars, are scaled to 3/16" to the foot, or S Scale, but they ride on O gauge wheels. The Bosco car in the front left is another Lionel model, a "Scout"-type boxcar also built to approximately S scale proportions but on O gauge wheels. These front cars are typical of what many hobbyists consider to be O27 cars - those that can easily navigate the tightest of O gauge curves. However, all four of these cars, including the Auburn Models true 1/48 boxcar, can easily navigate O27 curves.

The Challenge of Proportion

The challenge then, of 3-rail O gauge modeling, is to find cars and locomotives that are proportionally similar and run them together. This is mainly accomplished through time, experience, research, and a bit of trial and error. Unfortunately, most manufacturers offer models proportioned to various scales among their O gauge offerings. For example, Lionel's F-3, GP-7, and NW-2 diesel models are very close to true O scale. Their FA diesels, however, are closer to 1/55 scale. Similarly, Lionel made 4-6-4 steam locomotives that varied from true O scale, like the famous #700E, to the roughly 1/55 scale #2055 Hudson, and the 6-8-6 steam turbine locomotive scaled out to roughly 1/64 scale! Generally speaking, however, the smaller diameter curve the train will handle (27" vs 72" for example) the smaller the proportion of the model. Conversely, if you are looking to model true O scale in 1/48 proportion you will likely be limited to those models that can navigate O42 curves and larger.

Track Type: O or O27?

This diagram from a postwar Lionel instruction sheet
incorrectly identifies the diameter of Standard O curves
as 30" rather than 31".

Further complicating things is that there are two main types of O gauge tubular track: Standard O and O27. Both types are the same gauge (1 1/4") but the rails differ in height and length with Standard O having the larger dimensions in each case. O27 derives its name from the diameter of a circle of track measuring 27" vs. the 31" of Standard O. O gauge hobbyists refer to other curve diameters by number as well, such as O42, O54 and O72 denoting curve diameters of 42", 54" and 72" respectively. If you are not totally confused yet, consider that all of these track diameters are available in both O27 and O31 track profiles!

Which should you choose? It depends on your tastes and your needs. I choose to use O27 track because it is less expensive, readily available, and the lower track profile looks more realistic. On the other hand, Standard O track is more durable and mates with most brands of modern track systems and flexible track such as Gargraves and Atlas O. 

Whichever you choose, Happy Railroading!