What scale is OO gauge

If you have an OO gauge railway you’ll want to get suitably sized models and rolling stock so what scale models are appropriate for OO gauge?

OO gauge is the most popular model railway track in the UK and made famous by its largest producer Hornby.

The track is 0.65 inches or 16.5 mm wide, rail to rail, which works out to a scale of 3.5 mm to 1 foot but strangely the rolling stock and models are to a different scale.

The shells of locomotives, wagons and passenger cars for OO is actually 4mm to the foot or 1:76.2.

So when modelling for OO gauge, use this as the scale.

The reason for the difference between the scale and gauge for OO gauge is down to history as explained here. Simply put, when OO railways were created by Bing in 1921, the most popular trains were in another size: HO.

To keep compatibility with these existing products — and so keep costs low — OO was designed to use HO width track. However, because British locomotives were smaller than European engines there wasn’t enough space inside the models for the motors at this scale so shells of OO rolling stock was created in the fractionally larger at 4mm to the foot scale.

Summary: OO is 4mm (0.15inches) to 1 foot (1:76) running on HO scale 1:87 / 3.5 mm to 1 foot track, 0.65inches or 16.5 mm.

And it’s been like that ever since.

> 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 modelrailwayengineer.com. 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,

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