Last Updated on May 13, 2022 by Dave Farquhar
Model trains come in a variety of sizes to fit the space you have available. Or, to cram more stuff into the space you have available. Here are the common sizes of model trains, or, if you prefer, model train scales.
Sizes of model trains, or any other model, are measured in scale. Scale is a ratio of the model’s size relative to the real thing. Sometimes people will refer to gauge as well, which relates to the track, rather than the train.
G scale
G is more of a collection of scales than a true scale unto itself. The largest G scale trains are 1:22 scale and the smallest are 1:32 scale, with 1:29 in between. They all run on the same track, but the sizes vary a bit from brand to brand.
Let’s just round it to 1:24 scale, meaning a half inch represents a foot in real life. It makes the math easier. So a 40-foot box car is about 20 inches long in G scale. G scale trains are large, so enthusiasts often run them outdoors, where space is more plentiful.
G scale was really popular in the 1980s and early 1990s, but it faltered somewhat in recent decades. Popular makes included Aristocraft and LGB. Today, Bachmann and Lionel are the two brands that are easiest to find.
The large, inexpensive train sets available in retail stores during the holidays are usually G scale. Inexpensive G scale sets often run on batteries and use plastic track. Frequently they operate by simple remote control.
O scale
O scale is another oddball, kind of like G scale. In the United States, true O scale is 1:48, meaning a quarter inch represents a foot in real life. If you want more confusion, in continental Europe it’s 1:45 scale and in the UK it’s 1:43 scale. They’re pretty close in size but not exact.
A 40-foot box car is about 10 inches long in O scale. People closely associate O scale with Lionel, and until the early 1990s, Lionel didn’t pay much attention to scale. Many Lionel “O scale” trains are really closer to 1:55 scale or even 1:64 scale while running on the same track that a true O scale model would. Here’s more on those smaller cars, often called O27.
O scale also tends to be rather large. A circle large enough to handle a true O scale train is six feet in diameter, which is one reason Lionel played fast and loose with scale for decades. People wanted big trains but they didn’t want to dedicate hundreds of square feet to it. Even today, while Lionel has full 1:48 scale trains for dedicated hobbyists, they sell smaller trains for people who are willing to live with some compromises in scale fidelity. The smaller trains often are called O27.
Lionel is a good choice for kids, since the large trains and large couplers are easier to put together than smaller scales. Small children often get frustrated quickly with HO scale.
S scale
S scale is 1:64 scale, the same as many diecast cars. People most closely associate it with American Flyer trains from 1946-1968. In the 1950s, O and S scale were the most popular sizes of model trains, though they faded in the late 1950s. S scale grew popular partly because you could put a realistic-looking train with a visually interesting track layout on a ping-pong table and it would run OK. It gave a nice balance of size and realism.
Lionel bought American Flyer in 1969, and resumed production in 1979. S scale trains are still available today, even though they aren’t as popular as many other scales, and nowhere near as popular as they were in the 1950s. It’s also easy to find vintage American Flyer trains, of course.
In S scale, 3/16 of an inch represents one foot. So a 40-foot box car in S scale is about 7 1/2 inches long.
OO scale
OO scale never caught on in the United States, but in the UK it’s the most popular size of model trains, dominating there the way HO scale does here. OO scale is 1:76 scale, about halfway between S and HO scale in size, and it uses the same track as HO scale in the rest of the world.
In OO scale, 4.5mm represents one foot. A model of a 40-foot box car measures about 6 1/4 inches in OO scale.
HO scale
HO scale is the most popular scale for model trains, by far. It’s 1:87 scale, approximately half the size of O scale. Like S scale, it permits a decent sized layout on a ping pong table. But unlike S scale, you can fit something moderately complex on a 4×8 sheet of plywood without any awkwardness. HO scale really took off in the late 1950s as Lionel and American Flyer stumbled.
HO scale trains are the easiest size of model trains to find, due to their popularity. Most hobby shops that deal in trains have a good selection of HO scale. Popular makes include Athearn and Bachmann.
In HO scale, 3.5mm represents one foot. So a 40-foot box car in HO scale is about 5 inches long, if you round off.
One caveat: HO scale slot cars are 1:64 scale, which is the same as S scale in model trains. They’re bigger than HO scale trains.
N scale
N scale is the second most popular scale for model trains. It’s 1:160 scale, approximately half again the size of HO scale. With N scale, it’s popular to fit a simple but interesting layout inside a coffee table. Alternatively, you can build a large layout and put more mileage on it.
N scale trains are nearly as easy to find as HO scale trains. Most hobby shops that carry HO scale trains will also carry N scale trains. They may not have quite as wide of a selection. Popular makes include Bachmann and Kato.
In N scale, 1.9mm represents one foot. So a 40-foot box car in HO scale is about 3 inches long.
N scale is popular with hobbyists but the difficulty of coupling them makes it not as good of a choice for children. As modelers age, they tend to move toward the larger scales as well.
Z scale
Z scale is the smallest of the popular commercially available scales or sizes of model trains. It’s 1:220 scale, somewhat smaller than N scale. Z scale allows you to fit a layout inside a coffee table, or simply cram more scale miles into a larger layout than N scale would allow.
Z scale is less popular and widely available than HO, N, or O scale. If you ask a Z scaler, it’s more popular than S scale, but if you ask an S scaler, they’ll say it’s less popular.
In Z scale, 1.38mm represents one foot. So a 40-foot box car in Z scale is less than 2 1/4 inches long.
Converting from one scale to another
Plans in books and magazines often are printed in HO scale or S scale. What if the plan for something you want to build isn’t in your preferred scale? You can convert the dimensions. Here’s a scale conversion chart.
Matching items to your train scale
Now, let’s say you have an existing collection of vehicles, toy buildings, holiday villages, or figures. Do any of them match the train scale you’re considering? You can figure that out with a bit of fairly simple math. Here’s how.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.
I wish US use the metric system so no need to say something like “1.38mm represents one foot”
I find the metric system easier, but the United States is notoriously slow to change. Oddly enough though, the convention of using x quantity of mm to represent a foot originated with the British.
How do you decide what vehicles go with each scale? I have many vehicles but I don’t know which train they fit best? I acquired a huge collection of vintage train stuff.
I have a blog post on determining scale based on its measurement. I’ll add a link to the blog post. Thanks for the idea!