Model railway gauge: the definitive guide

How does gauge influence a railway’s look and feel? What’s the difference between gauge and scale? How do different gauges compare? In this comprehensive and definitive FAQ guide, we’ll demystify these pivotal concepts and more, offering clarity for both newcomers and seasoned hobbyists.

Understanding gauge: basics and distinctions

The track gauge plays a pivotal role in a model railway, serving as the foundation upon which entire layouts are built. But if the results of the fun quiz I run here on ModelRailwayEngineer are anything to go by it’s still a very misunderstood issue. Here are answers to your most common questions.

What is gauge?

Gauge in model railways is the measure of the distance between the inside of the rails on the track. It is one of the key measurements of a model railway and determines the track and trains used, the other being scale.

Model trains come in a wide array of gauges, each with its own unique charm and purpose. From the tiny Z gauge, perfect for those with limited space, to G gauge that’s often seen in garden railways. Choosing the right one depends on space, budget, and the level of detail and realism wanted.

What is the difference between gauge and scale?

Gauge and scale are distinct but intertwined concepts. Gauge refers to the distance between the two rails on a track, ensuring compatibility across different train models. Scale, on the other hand, denotes the proportion between the model train and its real-world counterpart>

For example, a 1:100 scale means one unit on the model represents 100 units in reality so a 1:76th scale train would be 76 times smaller than its real-life counterpart. While gauge ensures trains fit the tracks, scale maintains the model’s realistic proportions compared to full-sized trains. Both are vital for the authenticity and functionality of model railways.

However, there’s an intriguing discrepancy between scale and gauge for model railways: the scale of the track gauge doesn’t always match the scale of the train’s body.

This mismatch can arise due to manufacturing decisions, cost considerations, or the desire to fit standardized components. As a result, a train might appear either too bulky or too slender for its tracks, and incorrect when compared to the real thing, even if it operates smoothly.

One of the most well-known examples is the OO gauge trains. The standard gauge for full-sized railway tracks is 4 feet 8.5 inches (equivalent to 1,435 millimeters). OO gauge model railway track is 16.5mm wide, giving a scale of 1:87 for the track gauge.

The bodies of OO gauge trains however are scaled at 1:76.2, making them slightly larger than is correct for the width of the track resulting in trains look a bit oversized for the track they run on. HO gauge trains, which have the same track width, are scaled to 1:87 and so look more appropriate for the track.

How does track gauge affect the look and feel of my model railway?

The gauge you choose determines the size and scale of the track, trains and scenery on a model railway layout. For example, a larger gauge like O or G will allow for more detail but will require more space.

How many types of track gauges are there in model railways?

There are several common gauges in model railways, including Z, N, 009, HO, OO, S, O, and G, among others.

  • N Gauge: 9mm
  • OO Gauge: 16.5mm
  • HO Gauge: 16.5mm
  • O Gauge: 32mm (in the UK) or 1.25 inches (in the US)

Why is gauge important in model railways?

Gauge is the linchpin of model railways, defining the distance between the tracks and ensuring the compatibility of your trains. It’s the foundation that influences the size, detail, and overall look of your layout.

A correct gauge ensures that locomotives, carriages, and accessories align seamlessly, creating a cohesive and operational miniature railway world. Equally, it determines the space needed for a layout, has a significant bearing on the cost of the track and trains and determines the trains you can run – not all trains are available in all gauges.

Why are there so many different track gauges in model railways?

The diverse track gauges in model railways stem from historical and practical reasons. As real-world railways developed, regions like Europe, North America, and Asia adopted varying track widths, from the wide Russian gauge to the narrower ones in the UK. To improve authenticity model train manufacturers, mirrored these real-world variations.

With technological and manufacturing advancements and improved materials, manufacturers introduced even more gauges to cater for space constraints and preferences, such as the compact N gauge for smaller spaces or the expansive G gauge for garden railways. Hornby’s recent introduction of TT:120 is another example.

What are the most common model railway gauges?

The most common gauges of model railway track in the UK are N and OO gauge; in America and continental Europe HO and N gauge are the most popular. In a survey carried out by one of the UK’s largest model train websites in 2023, OO gauge was used by 64 per cent of railway modellers while 26 per cent built N gauge layouts.

How do I choose the right track gauge for my model railway?

This depends on the space available, the desired level of detail, budget, and personal preference.

For example, N gauge is great for smaller spaces, while O or G gauges are larger and can be more detailed but need a lot more space. Being the most popular in the UK, there’s a huge range of OO gauge rolling stock and models available and with a huge second-hand market it’s the cheapest to get.

Personally, I use 009 gauge as it allows me to get lots of track into an area that wouldn’t be possible with OO but the model sizes are large enough to see and enjoy which can be a problem with N gauge, as described here.

What are the cost implications of choosing one gauge over another?

The choice of gauge can significantly impact the cost of a model railway. Popular gauges like OO or N often have a wider range of products available, potentially offering more competitive prices due to higher production volumes.

Conversely, rarer gauges, such 009, can have a premium due to limited production runs.

Additionally, larger gauges, such as O or G, often demand more materials for tracks and scenery, potentially increasing costs.

Can I mix different gauges in one model railway layout?

Yes, some model railway engineers create “dual gauge” layouts where tracks of two different gauges run side by side or even share a rail. This can replicate real-world locations where multiple gauges exist. This is most often done where a mainline service modelled in OO gauge meets an industrial narrow gauge railway modelled in 009 scale.

It’s even possible to have track with 3 rails on it, allowing trains of two different gauges to run on it.

Frequently asked questions about specific gauges

What is OO gauge?

OO gauge has held a significant place in the model railway landscape since its introduction in the 1930s. With a track gauge of 16.5mm between the rails, it balances detail with size, positioning itself as a popular choice for those keen on exploring model railways without needing the space necessary for O scale.

The “OO” designation, often interpreted as “Double-O,” signifies the scale’s standing between the larger O gauge and smaller alternatives. When it comes to scale representation, OO gauge predominantly follows a 1:76.2 ratio in the UK.

Being more substantial than N gauge, OO gauge allows for a richer level of detail, capturing the nuances of actual trains and environments.  Its popularity guarantees a broad selection of OO gauge locomotives, carriages, tracks, and supplementary items from a range of producers.

What is N gauge?

N gauge trains are small, with a rail width of 9mm, but are beautifully detailed.

Introduced in the 1960s, N gauge has become a favoured choice among model railway enthusiasts. With a track gauge of 9mm between the rails, it strikes a perfect balance between intricate detail and space efficiency.

This makes it especially appealing for those venturing into model railways and who might not have the room for larger scales. I’ve built multiple model railways in it, particularly my Cornish-themed layouts that require long stretches of track and large landscape features (Cornish hills and valleys with their mines) and for which I wouldn’t have space to do so in OO gauge.

The term “N” originally stood for “Nine millimeters,” the distance between the rails. In terms of scale, N gauge typically represents a 1:160 ratio in the United States and a 1:148 ratio in the UK, meaning the model train and scenery are 1/160th or 1/148th the size of their real-world counterparts.

N gauge offers several advantages. Firstly, its smaller size allows hobbyists to create intricate and expansive layouts even in limited spaces. This means you can have longer train routes, more detailed scenes, and a variety of landscapes without needing a large area. Secondly, due to its popularity, there’s a wide variety of N gauge locomotives, rolling stock, track types, and accessories available from many manufacturers. However, it’s worth noting that the smaller size can also be a bit challenging for those with less steady hands or eyesight issues, especially when it comes to detailed work or handling tiny components.

What is Z gauge?

OO gauge train next to a Z gauge train for comparison

Z gauge is much smaller than OO gauge

Z gauge is among the smallest commercially available scales in model railways, defined by a track gauge of just 6.5mm between the rails.

The “Z” in Z gauge originally implied “zero” or the smallest size in model trains when it was introduced in 1972 by the German model train manufacturer Märklin.

In terms of scale, Z gauge typically operates at a 1:220 ratio, meaning the model train and its accompanying scenery are 1/220th the size of their real-world counterparts.

Its diminutive size means that even the most elaborate and winding railway layouts can fit on a standard table or even a briefcase! This makes Z gauge an excellent choice for those with very limited space or those who want a portable layout. The compactness of Z gauge doesn’t mean a compromise on detail; many Z gauge models are intricately detailed and beautifully crafted. However, the small size also brings challenges. Handling and assembling the tiny components require a steady hand and good eyesight.

Additionally, while there’s a dedicated community of Z gauge enthusiasts, the variety of available models and accessories isn’t as extensive as more popular scales like OO or N. Nevertheless, for those intrigued by the idea of a miniature world in the smallest of spaces, Z gauge offers a fascinating and space-saving entry into the realm of model railways.

What is 009 gauge?

Model Railway Engineer's 009 model railway layout

009 gauge, N gauge track; OO scale models.

009 gauge refers to a specific combination of scale and gauge. The “009” denotes a track gauge of 9mm, similar to N gauge. However, what sets 009 apart is its scale. While the track gauge is 9mm, the scale typically represents a 1:76 ratio (the same as OO scale). This means that 009 models are designed to depict narrow gauge railways in the real world that are approximately 2 feet 3 inches wide, using the same track width as N gauge but with larger, OO scale rolling stock and scenery.

009 offers a unique blend of narrow gauge charm with the more substantial size of OO scale models. Narrow gauge railways often have a distinct character, often associated with rugged terrains, industrial settings, or scenic tourist routes. Modelling in 009 allows enthusiasts to capture this character while benefiting from the detail and heft of OO scale models.

The combination of narrow gauge track with larger rolling stock can be especially appealing for those, like me, who want to create detailed and characterful layouts without needing as much space as standard OO gauge would require.

However, it’s essential to note that while 009 has a dedicated following, it might not have as extensive a range of off-the-shelf models and accessories as some other scales. But for those drawn to the allure of narrow gauge railways, 009 offers a delightful and detailed modelling experience.

What is gauge is TT:120?

TT:120, commonly known as “TT scale,” represents a model railway scale where every unit on the model equates to 120 units in reality, with tracks having a 12mm gauge. Positioned between the larger OO/HO scales and the smaller N scale, TT offers a balance: it’s compact enough for limited spaces yet retains a commendable level of detail. This scale allows for intricate rail networks and sceneries without needing as much room as OO/HO.

However, TT has its challenges. It’s less popular than OO/HO and N gauges, making it harder to find models and accessories. And while its size is an advantage, some modelers might find the smaller trains trickier to handle, especially for delicate tasks.

What is the width of a full-size train track?

In the UK, North America, and most Standard gauge track around the world, the rails are 4 ft 8+1⁄2 in (1,435 mm) apart, as used by George Stephenson for the Liverpool and Manchester Railway in 1829.

Troubleshooting track gauge problems

Can model train track gauge be wrong?

Yes, the gauge of model train track can sometimes be too wide or to narrow causing trains to derail.

This can occur if the track is damaged during installation, particularly if it is bent, occasionally due to extremes of temperature when the rails may expand when hot, or occasionally due to errors in manufacturing. If you have problems with consistent derailing on a particular part of the track, it’s worth checking the width between the rails.

It’s always worth checking the gauge is correct if using second-hand track.

How to check the width between rails?

Checking the width of model train track with a digital caliper.

It’s easy to check if the track is the correct gauge with a digital caliper.

If you suspect the rails of your train track aren’t the correct width, causing derailments, you can check the spacing between them with either digital callipers or roller gauge.

For O gauge track, the rails should be 32mm apart, for OO/HO gauge track they should be 16.5mm apart, while N, 009 and HOe must have a gauge of 9mm and Z gauge track is 6.5mm wide.


That concludes this round up on model train gauges. I hope it’s been useful and helpful. If you have any other questions on the topic of track gauge, add a comment below and I’ll do my best to answer it.

> A final, personal, note: I spend a huge amount of time testing, photographing, writing and researching techniques for these articles and pay for all the running costs of MRE out of my own pocket. If you found this article useful you can support me by making a donation on my fund-raising page. Thanks and happy modelling, Andy.


Founder of ModelRailwayEngineer, Andy Leaning

Andy is a lifelong modeler, writer, and founder of He has been building model railways, dioramas, and miniatures for over 20 years. His passion for model making and railways began when he was a child, building his first layout at the age of seven.
Andy’s particular passion is making scenery and structures in 4mm scale, which he sells commercially. He is particularly interested in modelling the railways of South West England during the late Victorian/early Edwardian era, although he also enjoys making sci-fi and fantasy figures and dioramas. His website has won several awards, and he is a member of MERG (Model Railway Electronics Group) and the 009 Society.
When not making models, Andy lives in Surrey with his wife and teenage son. Other interests include history, science fiction, photography, and programming. Read more about Andy.

Afflliate disclosure:The links on this page may take you to carefully selected businesses, such as Hornby, Amazon, eBay and Scale Model Scenery, where you can purchase the product under affiliate programmes. This means I receive a small commission on any orders placed although the price you pay does not change. You can read my full affiliate policy here. I also sell my my own ready to use, pre-made and painted buildings and terrain features. browse the range.
    • Hi David, yes but they’re hard to find now. Look for Gauge 1 models or 1 gauge. It has a track width of 1.75 inches or 44.45 mm. It was popular before WW1 but went out of fashion and I’m not aware of any manufacturers making it now. The trains and track pop up on eBay from time to time and that’s probably you’re best bet. Andy

Add Comment

Required fields are marked *. Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.