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Model Railway Scales and Gauges Explained

There are a huge number of variations of model train set gauges and model railway scales.

 The track gauge is the distance between the rails, and the scale is the size compared to real-life trains.

This variety of model railway gauges can be truly mind-boggling!

Knowing where to start can be the biggest challenge.

I have been building model railways since I was 12, and back then the only choice for ready-to-run models was OO gauge.

Since then there has been an explosion of new gauges and rail scales, along with a comeback of older popular gauges as manufacturers started mass producing locomotives and rolling stock in gauges other than OO gauge.

Hornby train gauges historically used the worldwide O Gauge standard, and currently, their range of OO Gauge tracks is compatible with PECO Setrack.

In this article I will cover the following topics:

  • An introduction to model trains
  • What are scales and gauges
  • 7 most popular choices in the UK
  • The pros and cons of each
  • How you can choose which one is right for you
At the end of the article are some links to explore some of the products available in the 4 most popular gauges

An Introduction to model trains

Model railways are sometimes dismissed as being toy trains, however, the hobby can be much more than that.

For some people, creating model landscapes and the model trains that run in them, is an art form.

The level of detail that can be achieved nowadays with model trains is amazing.

The detailed interior of a model signal box

Several manufacturers are producing incredibly realistic and highly accurate models, even down the correct positioning and numbers of rivet detail.

Scale models are faithful recreations of full-sized prototypes in miniature.

For the adult model railway collector, toy trains are a thing of the past.

Larger scale ride-on miniature trains fall into the category of model engineering and are outside the scope of this article.

The hobby is not just limited to trains and track, it also includes rail scale model train structures.

Scales and Gauges for model trains

Railway modelling has a wide variety of different scales and Gauges.

This can be confusing for someone new to the hobby.

In this blog post, we will explain the different scales and gauges used so that you can choose the right one for you!

Our window display combines both OO gauge and OO9 models in one layout

There is a growing range of popular scales and gauges available commercially.

In this article, we look at the most popular scales and gauges in the UK in 2022.

The track gauge is the distance between the two rails, while the scale refers to how big the trains are in comparison to the real world.

7 Common Track Gauges and model train Scales in the UK

  • N Gauge 2mm Scale
  • OO Gauge 4mm Scale
  • OO9 9mm track gauge and 4mm scale
  • O Gauge 7mm Scale
  • Gauge 1 - 1/32 Scale
  • SM32 - 32mm Gauge 16mm scale
  • G45 - 45mm Gauge 7/8 scale

model train gauges chart UK

This image shows N to SM32 gauges side by side

How big is 00 gauge?

The most common model train gauge used in the United Kindom is the OO gauge.

OO has a track gauge of 16.5mm and a scale of 1:76.2 or 4mm to the foot.

OO gauge scale represents the UK standard gauge full-size prototype.

Because of the confusion between scale and gauge OO gauge is sometimes incorrectly referred to as the OO scale.

OO gauge track dimensions vary based on the length of the track unit, or radius of the curve but the gauge remains fixed.

Benefits vs Disadvantages

  • OO gauge is the most common scale used in British model railways.
  • OO gauge models are typically less expensive than O gauge models.
  • OO gauge model railways can be easier to use than smaller scales.
  • The lengths of trains in OO gauge model railways can appear less realistic when compared to train lengths possible with smaller scales.
  • OO gauge model railways can be more difficult to fit into small spaces.

HO Scale

In the US HO is the most popular choice in model railroad scales.

The HO trains represent US standard gauge trains and are 16.51 mm wide and 12.95 mm tall.

The name comes from the fact that these HO scale models are half the size of O scale trains, which were once the most- popular scale type of model railway.

Because the Gauge of 16.5mm is the same as the OO Gauge HO Scale models can use narrow gauges on the same track as 4mm scale models.

However, HO scale accessories will look too small on OO Gauge 4mm scale models as OO models are slightly larger than the smaller scale of HO.

N Gauge

Another popular gauge option is the 9mm track gauge system.

N Gauge track has a scale of 1:148 or 2.117mm per foot for UK Standard gauge trains.

Standard Gauge N gauge train sets are much smaller than OO gauge, at just over half the size.

This makes them perfect for people who want to build a large railway but don't have a lot of space to do so.

N Scale is sometimes used to describe models of UK standard gauge prototypes running on the N gauge track.

Benefits vs Disadvantages

  • N gauge track is perfect for people who want to build a large railway but don't have a lot of space to do so.
  • N gauge models can be more expensive than HO or O scale models.
  • N gauge model layouts can be more difficult to build because of the small size of the track, locomotives and rolling stock.


Models of 2-foot Narrow Gauge prototypes using the same 9mm Gauge track as N gauge are known as OO9.

They use the same track gauge of 9mm as the N gauge track with slightly deeper rails and chunkier irregularly spaced sleepers.

OO9 gauge represents 2-foot narrow gauge railway systems.

Because its scale is still 4mm to the foot you can use it on the same scale ratio layout as OO gauge standard gauge models.

Industrial narrow-gauge railways were once a common sight across the UK.

Benefits vs Disadvantages

  • OO9 gauge track is perfect for people who want to build a Narrow Gauge prototype railway
  • You can combine OO9 Narrow Gauge and OO Standard Gauge railways in the same model as they are on the same scale
  • Fewer commercially available model locomotives and rolling stock

O Gauge

If you're looking for something in larger scales, an O gauge or 1.43 scale 7mm to the foot model of UK standard gauge might be right for you.

These trains are bigger than the OO scale, but not as big as the Gauge 1 locomotives or Garden Railways.

O gauge was the first standardised model gauge developed for clockwork-powered trains in the 1930s.

O Scale is sometimes used to refer to 7mm scale standard gauge model trains running on 32mm gauge track.

A model of a GWR 48xx tank loco in 7mm scale made in 2020 by Dapol

Benefits vs Disadvantages

  • O gauge railways can be very realistic.
  • O gauge models are typically much more detailed than N or OO gauge models.
  • Large enough to be used outdoors
  • Fewer commercially available O gauge locomotives and rolling stock
  • Realistic train lengths in O gauge railways require either large amounts of space or represent a small branch line.
  • O gauge models can be more difficult to fit into small spaces.

Gauge 1

Gauge I trains have a track gauge of 44.45 mm which at a scale of 1:32 is the equivalent of 4 feet 8/12 inches standard gauge track.

Marklin is the largest commercial producer of Gauge 1 locomotives and rolling stock at the moment.

They are based in Germany which means that most of their models are European outline rather than British outline.

Benefits vs Disadvantages

  • Gauge 1 models are very large and impressive.
  • Gauge 1 railways can be very realistic.
  • Electric powered gauge 1 model's often include syncronised steam and smoke effects
  • Live steam models look fantastic
  • Gauge 1 models can be very expensive
  • Fewer models of full size prototypes are available

Garden Railways

Outdoor railways are commonly 32mm gauge 16mm scale representing British 2 feet narrow gauge, or 45mm gauge 7/8 scale.

Commonly known as SM32, 32mm is the same track gauge as the O Gauge track.

An SM32 16mm scale diesel locomotive on our SM32 demo layout

G45 is not quite the same gauge as the Gauge 1 track, being slightly wider at 45mm with a narrow gauge look.

Outdoor railways are popular due to their ability to use live steam miniature locomotives.

The term G Scale is often used to collectively group large-scale model railways. Unfortunately, G Scale does not refer to any precise scale track or track gauge.

Benefits vs Disadvantages

  • They are perfect for people who want to build a large railway and have a lot of space to do so.
  • Allows the use of live steam locomotives
  • Larger sizes of locomotives are easier to work on
  • Much greater levels of detail are possible
  • Combines a love of model railways and gardening
  • Model trains are more expensive
  • Heavier locomotives
  • Requires more space

So what track gauges and scales are right for me?

  1. Choose the full-size prototype your wish to model. Either standard gauge, narrow gauge railways, or both.

  2. Decide where you physically want your finished model to stay. Think ahead in terms of accessibility as you grow older, all-year-round access etc.

  3. Try to visit a model railway shop or exhibition to see the sizes of each scale and gauge for real.

  4. Decide what size of model trains you can see to work with.

  5. Budget is a consideration, but it is better to build your layout over a longer period of time than choose the wrong scale because it is cheaper.

In Summary

No matter what your preference, there is definitely a model train scale and gauge out there for you!

If you're just getting started in the world of railway modelling then we recommend choosing a model train scale that is suitable for your budget and the amount of space you have available.

Once you've got a few model train projects under your belt, you can then start thinking about experimenting with different gauges and scales!

Another of our demonstration layouts using OO and OO9 under construction

We hope that this information has clarified some of the confusion surrounding model train scales and gauges!

If you have any questions, please don't hesitate to contact us. We would be happy to help you choose the right option for your needs.

Want to know more about building a model railway? read How to start a model railway - all you need to know

You may also like our article on creating model landscapes or to find out about tiny signs for you model railway

As you approach the start of track laying you might appreciate our article Model railway points - All you need to know in one place

Product links

Click here for N Gauge Trains Click here for OO9 Gauge Trains Click here for OO Gauge Trains Click here for O Gauge Trains