Model Railway Beginners Q&A: What’s the difference between scale and gauge

model railway track scaleIf you’re just starting out in model railways one question that’ll you’ll invariably want answering is what are scale and gauge? What’s the difference between them and should you worry about them?

When it comes to buying and running model railways you’ll often come across gauge and scale. These two innocuous-sounding words relate to the size of your model railway and although often used interchangeably they mean very different things and shouldn’t be confused.


I’ll start with Gauge, for no other reason than it’s the easier of the two words to understand.

Just like full-size railways, the gauge of your model railway measures the distance between the rails on the track.

There are four track Gauges commonly used in UK railway modelling. From largest to smallest these are:

  • 45mm Gauge: Commonly used for garden railways.
  • 32mm Gauge: Often very realistic looking but can be expensive. Known as O gauge.
  • 16.5mm Gauge: The most common track and engines in the UK, more commonly known as OO gauge.
  • 9mm Gauge: The smallest, allowing more track to be laid in the same area, known as N gauge.


LMS 4-6-0Scale is the ratio between the size difference of your model to its real-world equivalent. The models you see on model railways aren’t just shrunk until they look about right but are all accurately reduced versions of their real-life counterparts, with every part reduced by the same amount.

The common model railway scales being:

  • O scale – 1:48 Needs lots of space and great for kids as the parts are big enough for children to handle easily. Works with 32mm gauge.
  • OO scale – 1:76  By far the most popular in the UK and uses 16.5mm gauge.
  • HO scale – 1:87  This size offers highly realistic layouts within a relatively small space, not as popular in the UK as OO but works to the same gauge.
  • N scale – 1:148 or 1:160 The second smallest train size and my personal favourite as it allows for great scenery but the small size makes it sometimes difficult to work with and the engines and parts aren’t as common or cheap as OO and HO. Runs on 9mm gauge track.
  • Z Scale 1:220 The smallest commercially available scale. Similar to N but much smaller. See my review of a Z gauge starter set.

So is it Scale or Gauge?

Now you’d be forgiven for thinking that if every object in a model railway was shrunk to the same scale then the tracks would be scaled down to the same degree as the rest of the set so the rails would be proportionately the same distance apart as buildings and figures are to the train.

Sadly not.

For a variety of reasons, the scale factor used to get set the distance between rails is often slightly different to the scaling factor used for the rest of the models so we end up with railway scale and a track gauge.

And, it’s possible to buy two trains with the same gauge but with different scales. OO and HO scales being the most obvious. These both use the same Gauge of track – 16.5millimeter – but OO models are slightly larger than HO (HO standing for Half O).

In most cases this difference is hardly noticeable but if you’re a stickler for accuracy and want your railway set to look just right it’s always worth checking that your purchase has not just the right gauge for your track but the same scale ratio as the rest of your layout.

TIP: If you’re looking for a guide to tunnel sizes for different sizes, Elgin Model Railway Club have done a great guide here

This post is part of my beginner’s guides. For more like it see my guide to Hornby how to guides and the top 4 best model train sets.

> 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.

 Picture: Track, J. Rygh.




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 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,
  1. OO Scale is 1:76, not 1:87 as you claim above. I’m surprised no-one has commented on this before.

    OO Gauge
    4mm to 1 ft, 1:76 scale
    16.5mm gauge
    OO is by far the most popular gauge in the UK, although the gauge is 15% under scale.

    HO Gauge
    3.5mm to 1ft, 1:87 scale
    16.5mm gauge
    The same gauge as OO, but with the smaller scale the gauge is in correct proportion to the scale.

    • Andy, thanks! The page was updated recently swapping the order in which the gauges are listed, HO and OO changing. I must have copied/pasted the OO and HO lines wrong then hence why it’s not been commented on previously. My bad. Thanks for pointing this out.

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