So what’s all this talk about gauges and scales?

If you guys are the “O” scale guys, what is O scale?


We are about to geek out here, read on at your own risk!

When miniature train builders started building their miniatures well over one hundred years ago, few (if any) were interested in building models of specific locomotives, but rather freelance miniatures, toys or even test platforms for locomotive ideas. Many of these were live steam powered, however many were spring wound toys. As they were one offs there was no need for any standardization, but as miniature trains became more of a hobby, builders wanted to be able to run their latest build on their own permanent layout or even a friends track; hence a need for standardization. Today we have the NMRA and other groups setting standards and assume that the new locomotive we buy at the hobby shop will run on our track from our controller without going up in smoke. (unless equipped with a smoke generator)


On February 1st, 1899 a subcommittee of the Society of Model Engineers recommended five standard model railroad gauges (spacing between the rails) numbered 0,1,2,3 and 4.

0 Gauge

1 1/4 inch

1 Gauge

1 3/4 inch

2 Gauge

2 inch

3 Gauge

2 1/2 inch

4 Gauge

3 inch


There were also several large gauge’s used for live steam “ride on” models that were standardized to 4", 5", 7 1/4“, 7 1/2”, 10” and 12” gauge.

Enter problem number one. Notice that there is no scale here. Again, there was little interest in scale at the time, Lionel became famous for their O gauge toy trains at the time, and few of these miniatures were even close to an accurate scale. However anyone wanting to model to a scale could figure out the ratio of the gauge of the prototype vs. the miniature gauge to find the proper scale. Which begs the question of what is the gauge of the prototype? Scores of prototype gauges were used over history from 18 inches to well over five feet. But the “standard” gauge in the US is 4' 8 1/2”. 

Enter the second common problem for the scale builders. Right from the beginning builders rounded off the standard gauge to five feet. Close enough and it keeps the math simple. Close enough? Scale builders never think close enough is ever close enough. However, because of this “cheat” O scale was standardized as 1:48, which is 1/4 inch to the foot and making the standardized gauge 5 feet, which is just a bit wide. Sucks, but there it is. Some scale fanatics model “O” to 1:43.5, known as “proto 48”, to solve this problem.

Also note that while the common usage is to call the gauge “O” (the letter) scale, the original nomenclature was “0” (the number).

Enter problem number three. If you build to fit a standardized gauge, when you build a narrow gauge train, say three-foot gauge, the model is built to a larger scale so it can run on the same track. Here again the scale builder is interested in having accurate scale, and if all of your trains are built to a different scale just to run on the same track, well that’s unacceptable. However in the larger gauges, 1,2,3 and 4, as well as the very large live steam models, this is still the standard practice. (Much to the chagrin of many a large scale modeler who may have five scales running on the same track). 

There is a better way however. Enter the narrow gauge model gauges based on scale. In “O” scale, we have several gauges, and the “O” Scale Guys have modeled in pretty much all of them. These have an “N” in their name to indicate a narrow gauge prototype. So three-foot narrow gauge prototype is modeled in 1:48 scale as On3 on a 3/4” gauge track.  This way an O scale layout can have several gauges, all in the same scale, each running on its own track, or even dual gauge track. The O Scale Guys have built in On18”, On2, On30”, On3 and O standard. The MRS layout had O standard, On3, On30” and On18”. All in the same scale running together. A mix of scales would look ridiculous.

OK so let’s get back to scales. Soon there was a need for smaller scales than O scale, and the trend has been to come out with smaller and smaller scales as technology permits.

In Brittan a scale was created called 00 (pronounced double oh) at 1:76.2. In keeping with other machinist gauge standards for things like screws, when the numbering system bottoms out at 0 the next size below that is 00. Then 000 and so on. The 00 scale is still widely used in the UK. But in the US, as 0 scale was now known as O scale, a new size, more or less the same size as 00, was created called HO. (Half O) and HOn3 for narrow gauge. As half O scale would have been 1:96, and as 1:48 was always a bit off, HO was standardized to 1:87. About half the railroad models built are modeled in HO and 00, far and away the most popular scales. They more or less work together, but not always well.

There was also a scale between these two, S scale at 1:64. For the most part this was a throw back to the idea of standardized track gauge without a real goal of accurate scale, but it has generally been much more scale accurate than the toy trains built in O scale. And there is an off-shoot, Sn3. The Sn3 crowd is a serious crowd, modeling accurate narrow gauge models in a size very similar to HO standard gauge that most people can fit in a smallish space.

Anyway, there is a bunch of smaller scales, and smaller gauges. TT and TTn3, or Table Top, at 1:100 never really took off well. N and Nn3 at 1:160, very popular, Z at 1:220, X at 1:304.8, and T at the microscopic 1:450. And an army of odd scales for the cultish out there: scale3, Q, P4/S4, EEM, EMF, EM, QO, HOO, OOO, K and QOO. Well so much for standardization, but for the most part standardizing has worked. 

The O scale Guys have modeled mostly in O scale, it is our most satisfying modeling experience.  However, we also model in other scales for various reasons. Alan has modeled in N scale in order to fit a lot of layout into a small space. Dale models big 50’s era in HO so that he can run 100 car trains. Hard to fit in O scale. And we have all modeled for the huge 1 gauge. It’s great to build in this huge size where details can really be taken to a high level. Yet there is a dark side to this scale, or should I say family of scales.

As mentioned earlier in this article, 1 gauge is a track size. And depending on the gauge of the prototype, five different scales are common in this gauge. They generally run well on any 1 gauge track, unless a model of a large prototype can’t navigate a sharp turn on a smaller layout generally intended for a model of a small narrow gauge prototype. 

Early on the 1 gauge scale builders built in 1:32 scale, and this scale is commonly referred to as 1 scale. But a quick trip to the slide rule (remember slide rules? For those of you under 40 think calculator) reveals that here again the standard gauge has been cheated a bit to keep the math simple. The correct scale for standard gauge modeled to a 1 3/4” inch gauge is a challenging 1:32.28571428751. Now that's not far from 1:32 but some standard 1 gauge modelers cheated the other way, scaling to 1:29 scale.  Which makes their prototype gauge 43.5, or 5 full inches too narrow. Which is a way bigger cheat, but making the models noticeably larger and many modelers like BIG. But the 1:32 and 1:29 look silly together, so it’s better to not mix these scales in the same train. Even keep them apart on the layout unless you want the mash up look. (yuk)

There has been another reason for the use of 1:29 scale. In machining there is a thing called a reduction pantograph. Molds for plastic models are milled with this device. A pattern model is built in wood in an oversized scale, and the pantograph follows this model carving a reversed mold, and because of the reduction system on the pantograph the mold is carved smaller than the pattern model. So a large pattern model can be built, say in 1:8 scale, and the mold reduced by a factor of 3 with the pantograph making a plastic model in 1:24 scale. The pattern being much bigger than the finished model is much easier to build. HO scale model patterns are built in 1:29 and reduced by 3 to 1/87. Meaning that most of the HO models have a master pattern somewhere in 1:29, which can by milled into molds without reduction making a 1:29 scale plastic model. For years 1:32 was the predominant scale for #1 scale standard gauge, but now 1:29 is much more dominant, even for brass models and live steam models. 

Enter G scale! A German company, LGB (Lehmann Gross Bahn,  or Lehmann large railway), entered the market with trains intended for outdoor use, or garden railways, with the designation G scale. (for garden) These were models of small one-meter gauge German models and so the scale used was 1:22.5. (1 meter=39.3700787 inches scaled to run on 1.75 inch #1 gauge track, 39.3700787 divided by 1.74 = 22.49718782857 (22.5)

So these meter gauge trains are accurately scaled, and very popular in Europe, but as demand rose in the US for American prototype, rather than build American 3 foot gauge prototypes, they cheated (here we go again) making these models in 1:22.5 so that they would look good with the European models assuming that the Europeans would also want to run these American models. For the most part this looks OK, 3 foot is close to meter,  but lets face it, European trains look silly mixed with American trains. Had LGB wanted to make accurately scaled American 3 foot gauge trains, the proper scale should have been 1:20.5. But here again, mixed scales look bad together, and 1:20.5 is really BIG, so they cheated the gauge making western 3 foot gauge trains in meter gauge. (John Ford is rolling over in his grave).

Oh, but it gets worse!! Many US manufacturers built their 3-foot gauge American prototypes in 1:24 scale. WTF? Here’s the thinking, or lack there of. As many Americans had standard gauge trains in 1:32 on their #1 gauge layouts, and as most early standard gauge freight cars were 40 feet long, and as most 3-foot gauge freight cars were 30 feet long, if you modeled standard gauge in 1:32 and 3-foot in 1:24, the scale freight cars were the same length, and about the same height, so you could mix standard gauge and narrow gauge cars in the same train and it didn’t look all that strange. And there wer lot's of models of cars and other things available in 1:24 to use with the train models. Right….. Anyway, that’s the way things were for years. Some modelers, like our own Don Henriksen, were so freaked out that they re-gauged their 1:24 stuff to 1.5 inch gauge. It couldn’t run on any #1 gauge layouts, but at least it was accurate. And many of these 1:24 scale models (1/2 inch scale) were awesome!


Check out Don’s scratch built drop bottom Gondola in 1/2-inch scale, 1.5" gauge. (There are more photos of this on the locomotives and rolling stock pages.)

And now, enter Fn3! All of this crap was settled when Accucraft  started building in Fn3 and Bachmann trains followed suit. Fn3 is modeled in the HUGE 1:20.3 scale for #1 gauge track. Also, these are very accurate models, correct wheel sizes, correct height, and mostly correct wheel flanges. Most of the earlier scales were to tall with over sized wheel trucks so they could go through sharper curves and stay on the track. Most of these clean up well with new trucks and couplers and a bucket of detail parts, but the new Accucraft and Bachmann models are great right out of the box. And can be good “filler” around your contest winning scratch built models.

But the gauge 1 fans have a real mess with five scales that look horrid when mixed together. So just don’t mix them. Think of them as matter and anti-matter. See, I told you we were going to geek out!!


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