Which is Bigger HO or O scale?

Finding the right size model train set can be a tricky process. With loads of different sizes to choose from it’s easy to lose sight of which ones are most suited to your vision for your own setup. The two most popular–HO and O scale–are often mistaken for being one and the same even though there are drastic differences between them. So, which one is bigger, HO or O? 

O-scale model trains are bigger than their HO counterparts. In fact, HO literally means “half O scale.” This can become confusing however because HO scale model trains aren’t actually half the size of O scale model trains. Instead, they are just close to half the size of O scale. 

If you’re curious about model trains and their sizes, this is the place to be. In our guide below, we will take a deep dive into the differences between O and HO trains. We’ll discuss the sizes of each along with facts about them relevant to those who are looking to get into model railroads. Additionally, we’ll discuss implications like which ones tend to be more popular and why.

brands of model trains

What’s the Difference Between O and HO Scale Train Sets?

So what exactly is it that distinguishes O scale trains from their HO counterparts? Is it just their size or are there more differences that need to be taken into account?

Below, we’ve broken down each of the major differences between O scale and HO scale model trains so you can decide which is right for your setup: 

  • Size: The most apparent difference between the two scales is their size. In the next few sections we will go into greater detail as to how big each scale really is, but for now, suffice to say that HO scale trains are a little over half the size of O scale trains. That’s actually how they got their name, as HO stands for “half O scale.” 
  • Track gauges: The gauge of each train’s tracks refers to how far apart the rails are. For O scale trains the gauge is going to be wider than that of HO scale. This is because the O scale trains are larger and require more space to run properly. 
  • The voltage required to run: To actually get your train rolling, you’re going to need some electricity. Still, depending on whether you choose O scale or HO scale, you may need a different amount of voltage. The average O scale train runs on about 18 volts. HO, on the other hand, only requires about 16 volts to function properly. 

As you can see, there are more differences between HO and O scale train sets than just their size. You’re going to need a different set of rails and very likely a different power supply as well. Of course, when you create additional pieces to make your setting look right, they will be different sizes as well. 

What’s the Size of an HO Scale Train?

We’ve talked about how HO scale trains are smaller than their O counterparts but as of yet we haven’t really gone over what their exact sizes are. So let’s start with HO. What’s the size of the average HO scale train? 

HO scale trains have a ratio of 1:87 when compared with the real thing. This essentially means that if you lined up 87 HO trains their collective size would be roughly the same as the real deal. 

When it comes to the exact proportions you can expect from your HO scale train, they may vary but do come around to an average. Most HO scale trains are going to have locomotives that are 56 mm tall and about 35 mm wide. Meanwhile their train cars will be somewhere between 140 mm and 75 mm long. 

fast model trains

What’s the Size of HO Gauge Tracks?

Another important component of your model train set is the tracks themselves. Like the train’s scale they also have designations for their size. In this case, that designation would be HO gauge. So what’s the size of HO gauge tracks? 

The rails on HO tracks are about 16.5 mm apart. This is actually the same width that OO scale train tracks are as well, making them cross compatible.  

What’s the Size of an O Scale Train?

Now let’s turn our attention to the larger of the two scales we’re taking a look at. If an HO scale train set has a ratio of 1:87 when compared with the real thing, what ratio does an O scale train–that’s meant to be roughly double the size–have? 

O scale trains have an average ratio of 1:48 when comparing them to the real thing. That said, it’s important to note that they can have a ratio that dips down as low as 1:43 in some cases and aren’t all exactly the same size.  

An important caveat here is that depending on the company you buy from, you can find trains that are labeled O scale but are way outside the normal ratio. For example, the company Lionel has marketed trains as O scale even though they had ratios like 1:64 or 1:55.

While the ratio of these “O scale” trains falls far away from the average, they still run on tracks with the same gauge as other O scale sets. So if you see a set like this, just know that while it might not be the typical size, it should still be able to run on the same tracks.  

lionel trains
Marine 69-71

What’s the Size of O Gauge Tracks?

If O scale train sets are larger than HO it stands to reason that they would need wider rails as well. So what exactly is the average size of O gauge tracks?

The rails on O gauge tracks are about 30 to 33 mm apart from one another. Like the scale, this is roughly, though not exactly, double the size (in width) of HO gauge tracks.  

Do O and HO Scale Sets Require the Same Voltage?

To get your train actually moving you are going to need a power supply with the appropriate voltage. Still, depending on what scale set you have you may need a different amount. 

O scale sets require more voltage than HO scale sets. This is, of course, in large part because they have more material that needs moving. 

What Voltage Does HO Scale Typically Run On?

While one can pretty much guess that HO scale sets–being the smaller of the two–will require less voltage, that doesn’t tell us exactly how much less. So, what voltage does an HO scale train typically run on? 

HO scale model trains tend to run on about 16 volts of electricity. This is great because it’s really not a whole lot considering what you get out of it. 

What Voltage Does O Scale Typically Run On?

Turning our attention towards the larger O scale sets, let’s take a look at what exactly they run on. 

O scale trains tend to run on about 18 volts of electricity. While that may not seem like a significant difference compared to HO, it really adds up over time. 

Which is More Popular: HO Scale or O?

It’s no secret that HO and O scale train sets are two of–if not the–most popular sizes available on the market. Still, if we put them head to head, which one comes out on top as the more popular scale for model trains?

While at one time O scale trains were the most popular size available, they’ve been slowly overtaken by HO scale sets since the late fifties. In fact, HO scale sets are not only more popular than their O scale counterparts, they are more popular than any other scale as well. This is the case for a number of different reasons. 

Below we’ll dive into exactly why HO scale trains have become and remained so popular for so many years, despite being smaller than their O scale competition. 

old lionel trains

Why is HO Scale So Popular? 

So now that we know HO scale trains are the most popular available on the market we are left with one question. Why? Why have HO scale trains become and remained so popular over the years?

Below we’ve broken down four of the biggest reasons why HO scale has been and remains more popular than O scale or any others:

  • Convenient size: With larger scale trains–like O or G, for example–comes the need for a larger space to set up or store them. HO scale trains, however, are great for saving space while still having an intricate, detailed setup. 
  • The level of detail: Hand in hand with the size, is the fact that HO scale trains can be highly detailed. On some of the smaller scales–like N, for example–it can be hard to get those fine details to stand out. HO scale trains, on the other hand, are just small enough for convenience and just large enough to go crazy on the details. 
    • Require less voltage: HO scale trains can save you some electricity in the long run because they require less voltage than their larger opponents. 
  • Variety and availability: HO scale model trains are the most commonly produced because of their economic viability and popularity. As a result, it is easier to find a variety of different train kits, sets of tracks and props for a set up. The sheer variety offered by HO scale train manufacturers is a big part of why they remain so popular to this day. 

All of this is not to say that O scale trains aren’t popular, just that for a variety of reasons they have been surpassed by HO. That said, other scales like OO or N are growing in popularity and may one day overtake HO if people’s preferences evolve and change. Regardless, you should pick the scale that best accommodates your needs rather than going with the most popular. 

train on model railroad benchwork
Jonathan Lee

How Do Other Scales Compare to O and HO? 

While O and HO scale sets are some of the most popular out there, they aren’t the only ones available. 

Below we’ve broken down the scale and gauges of the other major train scales and how they compare to O and HO: 

  • Z scale: Z scale sets are far smaller than either O or HO. Their scale is set at a ratio of 1:220 and their track gauge clocks in at around 6 mm. This not only makes them smaller than O or OH, but smaller than all other scales and gauges as well. 
  • N Scale: N scale sets are also smaller than O or HO. The ratio of their scale is 1:160, while the gauge is set at 9 mm. They are the most popular of the much smaller sets. 
  • S Scale: While less common than O scale sets, S scale is perhaps one of the more comparable out there. Their ratio of size is 1:64–which if you’ll remember is sometimes labeled as O scale–while their gauge is 22.5 mm. 
  • G Scale: G scale is for those who believe bigger is better. They are far bigger than either O or HO with a whopping ratio of 1:22.5. Their gauge is set at 45 mm in width. 

There are pros and cons to each of these scales and no one can really claim to be the best. For example Z scale will save you the most space but it will be harder to put in those fine details. G scale on the other hand, has plenty of room for detail but it is a really space taker. 

So Really, Which is Bigger: HO or O Scale?

At the end of the day, O scale is roughly–though not exactly–double the size of HO scale, making it the larger of the two. This is because HO scale trains tend to sit at a ratio of 1:87 when compared with actual trains. Conversely, O scale train sets have a ratio somewhere between 1:43 and 1:48. 

A good argument can be made for preferring either one over the other. Now that you know all about the differences in their sizes and the basics of how their set ups operate, which one looks more appealing to you? 


Lifelong Rail Enthusiast and Owner of Worldwide Rails

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