What Scale Is OO? The Difference Between HO and OO Scales


Are you looking to get into railway modelling? Perhaps you are already a huge fan but just want to know some more about it? Whichever sounds like you, understanding the different scales is essential!

There's no need to stress about it anymore, we've got all the answers.

What Is The Difference Between The HO and OO Scale?

HO and OO scale are the most widely used scales or gauges in the model railway community. But it can get rather confusing as some people tend to talk about them as if they are the same. It's important to note that this isn't the case at all.

HO and OO are actually standardized sizes of both scale and gauge (the distance between the tracks) combined

The difference between the two comes down to size. The OO scale models are built to 1:76th scale while the HO scale models are built to 1:87th scale. In simple terms, if you were to push 87 HO scale modes together, the result would be the same size as the real deal. Likewise, if you were to cram 76 OO scale models together, the final form would be the same size as the actual train.

We should mention here that you can use HO and OO scale models at the same time. How? Because they both use the same track gauge (16.5mm, the width the separating the rails). Whether you are handling rolling stock, locomotives, tracks, or the copious accessories, you won't hit any roadblocks.

Having said this, the correct scale for the 16.5mm track is the HO option. When you use the OO scale with the 16.5mm track, it won't be true to scale, the train will be slightly larger, which allowed for more detail to be included in the early days of model railways, although with modern production techniques there need no longer be the difference in detail there once was.

The Handy Tables

Below, you can find two tables that set out the differences between them in an "at a glance" format. Perfect for those of you who are getting into this fulfilling hobby.

OO Scale


Track Gauge


Manufacturer Examples


16.5mm track

4mm to 1 ft

Hornby, Dapol, Oxford Rail, Bachmann Branchline

HO Scale


Track Guage


Manufacturer Examples



3.5mm to 1 ft

Atlas, Bachmann, Eureka, Faller, Kato, Lima, Powerline, Auscision

Can I Use HO and OO Locomotives and Rolling Stock At The Same Time? Will I Be Able to Connect Them?

Of course! They will both run on the same track happily, however, you might have to find some other couplings to successfully connect them to each other. This is due to the fact that HO manufacturers use different types of coupler to OO brands. You will also need to consider the slight difference in size, some designs will look fine together whilst others will look mismatched due to the size difference. But try it out and see if you like it. Make the hobby your own!

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