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.


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