One of the first questions a new member of the hobby asks is, "what is a scale and gauge?" This is a very important question to answer because choosing the right scale and gauge for your needs is important before buying your first model train.
Scale refers to the size of the model compared to the size of the prototype while gauge refers to the width between the tracks.
In model railroading, scale is most often denoted by letters and/or numbers. Each letter/number refers to a different size ratio compared to the prototype. For instance, HO scale is 1:87th the size of the prototype. Narrow gauges typically are referred to by their spacing in inches, or feet in the US. For instance On30 refers to O scale (1:48th the size of the prototype) trains running on 16.5mm track representing 30 inch gauge rails on the prototype.
Scales and gauges can also generally be separated into commercial and non-commercial categories. The "normal" scales and gauges have commercial support with ready to run and kit models. The "odd" category includes specialty scales and gauges that only a few modelers enjoy and do not have much, if any, commercial support.
For most people entering the hobby, the most ideal scale and gauge to model in is HO scale standard gauge. The majority of new models that are entering the market are in this scale and gauge. Minimum radius from a train set in this scale is 18 inches, making a 36 inch diameter circle. Overall, this scale has the best compromise between the size of the models and the real estate they take up in the house.
However, society is changing and undoubtedly the model railroading hobby will change with it just like it has in the past. If I were to guess, the age of the massive model railroad empires that take up entire buildings is coming to a close, being replaced by more modest train layouts and club layouts maintained by multiple people.
Common Scales and Gauges
Those getting started in the hobby will want to consider one of the following scales to build their first model train layout. With only a couple of exceptions, these trains will be running on the scale-equivalent of standard gauge track. There are some commercial narrow gauge options, but narrow gauge models are a niche within the hobby.
HO Scale (1:87th)
As already stated, HO scale is the most popular in the hobby. While it's hard to get exact figures, about 80% of modelers have HO scale trains as part of their collection. This scale has wide-spread manufacturer support including giants such as Atlas, Athearn, Walthers, ScaleTrains, and Bachmann. Due to it's popularity, most model railroad clubs and organizations make HO scale the centerpiece of their model train layouts.
There is one primary narrow gauge option, HOn3. While traditionally HO scale narrow gauge was considered unreliable, improvements in model making and new companies like Blackstone Models has made HOn3 viable even for beginners. Another option is HOn30, also called HOe. These are HO scale trains running on 9mm gauge track (N scale).
HOn30/HOe has a small following but little commercial support. Thankfully, the availability of N scale mechanisms and 3D printing means moderately skilled hobbyists can enjoy HOn30.
If you are just getting started in the hobby, consider collecting at least a few locomotives in HO scale. Even if this isn't the scale you settle on, having some equipment you can bring to clubs or superdetail and paint as one-off projects.
N scale (1:160th)
N scale is the second most popular option for model railroaders. Somewhere around 25% of hobbyists have N scale as part of their collection, keeping in mind that many hobbyists have multiple scales. The advantage of modeling in 1:160th scale is that the models are small enough to fit into compact spaces roughly 1/4th the area of HO scale.
Alternatively, using a smaller scale means a larger section of railroad can be modeled in the same space. If a bedroom can effectively model a branch line in HO scale, in N scale a section of mainline can be modeled in the same space. Multiple deck train layouts are also easier to make since there doesn't need to be as much separation between levels.
N scale does have a narrow gauge option, Nn3. However, few commercial models are made for this gauge and Z scale mechanisms are hard to come by.
Beginners can certainly start enjoying the hobby with N scale, though it isn't the best for children. Conversely, teenagers and young adults will be especially attracted to the compact nature of N scale.
O scale (1:48th)
O scale is the oddball of the model train hobby. Approximately 10-15% of hobbyists have some O scale in their collection. Its roots go way back to the origin of the model railroad hobby. What makes O scale unique is that it has three primary groups; scale models, hi-rail models, and toy trains. Scale models are actual, 1:48th models of the prototype just like the other scales and run on two rail track.
Hi-rail models are mostly 1:48th scale, but run on three rail track that can navigate sharp corners. Hi-rail models have compromises that allow even large locomotives to navigate 42 and 54 inch diameter curves. Finally there are toy trains, a lineage of toy-like models that go all the way back to the beginning of the hobby.
When it comes to gauges, O scale is also a bit of an oddball. The "standard" gauge used in O scale is 32mm, which is actually the equivalent to 5 foot broad gauge. True standard gauge in O scale can be achieved by following the Proto 48 standard. Hi-rail and toy trains run on 3 rail track that can range from 27 inch diameter tubular track to scale-like dimensional track from Atlas.
Additionally, there are narrow gauge options, including On3, On30 (On2-1/2), and On2. On3 and On30 have commercial support and are by far the most popular. On3 represents 3ft gauge trains while On30 can be used to represent anything from 3ft to 2ft gauge models.
Large Scale (1:32-1:13.7th)
Large scale trains are also unique in that they all use the same gauge track, 45mm, but models can be multiple scales. The benefit of this arrangement is that the same track can run all sorts of models ranging from mainline, modern trains to old narrow gauge trains. 1:32 scale is the correct size for standard gauge trains on 45mm track, although in the US 1:29th scale is more common.
Large scale trains have been on a downward trend because they are generally used outdoors in a niche of the hobby called "garden railroading". Younger people are not buying homes at the same rate as their parents, and I suspect this is the source of this decline. It is a shame though because garden railroading a markedly healthier, outdoor option for enjoying the hobby that can be combined with another popular hobby, gardening.
Anyways, narrow gauge options for large scale include 1:24th and 1:22.5th scale, representing meter gauge trains, 1:20.3th scale, representing 3ft gauge trains, and 1:13.7th scale representing 2ft gauge trains.
Commercial support has also been declining for garden trains, but there is hope that this trend will eventually bottom out and then bounce back, depending on home ownership rates.
S Scale (1:64th)
The last of the "common" scales, S scale runs 1:64th sized trains. Having a similar history as O scale, S can be broken down into scale, hi-rail, and toy-like categories. Generally, S scale trains are more consistently scale like though across the spectrum of models available, the main difference is the track, wheels, and couplers.
Also similar to O scale, S scale has an ultra-realistic niche called Proto 64. Narrow gauge options are available as well, including Sn3, and Sn2.
S scale has declined significantly in popularity alongside the other 'large' scale options. However, there is still commercial support. Sn3 narrow gauge models are especially a popular option, though these models are expensive to buy, 3D printing and home laser cutting gives this scale hope for a rebound with cottage industries.
Other Scales and Gauges
While these are the most popular, commercial options in the hobby, there is a plethora of other scales and gauges out there for hobbyists to enjoy. However, the learning curve is much higher for beginners because it involves primarily building models from scratch, sometimes even the mechanisms needed to power locomotives.
Some great options that are out there which can be especially appealing:
Gn15 (1:24th)
Gn15 is 1:24th scale models running on HO scale mechanisms. Representing very narrow gauge mining trains, estate railways, and agricultural railways. What's great about Gn15 is that a sprawling railroad in a large scale can be built in a very compact space. This is a popular option for building micro train layouts.
1:35n2 (Mn2 Scale)
A good introduction to this scale can be found in the Narrow Gauge and Shorline Gazette Nov/Dec 2021 issue. Created by Woodie C. Greene (author of the article), 1:35th scale is popular for military models and, by using HO/On30 mechanisms, realistic 2 foot gauge model trains can be created.
Z scale (1:220th)
Z scale trains are about 2/3rds the size of N scale and run in very compact spaces. Z scale does have commercial support, however there are not many people using this scale as their primary size of choice. The good news is that Z scale can be made to be reliable and even perform slow-speed operations. However, generally Z scale is considered a bit too small to be ideal for kitbashing and scratchbuilding.
OO scale
OO scale is popular in Britain but less so in the US. Using 16.5mm track, OO scale is actually 1:72, a popular scale for model cars, planes, and even small boats. OO models tend to be more robust than their HO scale counterparts, meaning they can be used outdoors in mild climates. OO models can be purchased in the US either by importing from the UK, buying from a select few distributors, or purchasing second hand equipment.
Sn42
This niche scale and gauge combination has great potential. Also using HO scale mechanisms on S scale models, Sn42 trains represent 3.5 foot gauge prototypes. At first this might seem to be an odd-ball gauge, but the reality is that 42 inch gauge prototypes. Logging and mining railroads often used this gauge, as did many streetcar and traction lines.
Japanese, South African, Australian and Nova-Scotia railroads also have a history of 42 inch gauge which makes this an appealing option for US modelers wanting to model foreign and exotic prototype railroads.
On18
On18 trains are like the smaller cousin to Gn15 trains. Using N scale mechanisms, On18 trains can also representing mining and industrial narrow gauge prototypes in extremely small spaces. Train layouts can be as small as a single square foot!
Conclusions
There are dozens of options to choose from when picking a scale and gauge for a model railroad. Understanding what you want to model and how much space you have will be the biggest factors in determining which scale and gauge will be right for you.
Do you want to model a class I railroad in a bedroom? N scale is right for you. How about a switching layout in an urban industrial setting built in the garage? O scale would be an excellent option. Don't have enough space for a regular sized layout but want something kinda fun an whimsical? Gn15 or On18 would fit the situation perfectly.
