OO scale is the most popular model railway scale here in the UK and there's not a huge difference between OO and its European HO scale equivalent. But will OO scale locomotives run on HO scale track?
What's the difference between OO scale and HO scale.
For reference and completeness, it's worth taking a look at our what is OO gauge article to get a full understanding of what it actually means. And our in-depth article explores the differences between the two scales. But the easiest way to compare the two scales is to look at their scale ratios:
- OO gauge (scale) = 1:76
- HO scale = 1:87
That means, for each scale, to convert a real-life measurement to each scale we either divide it by 76 or 87 depending on which scale we're working in. Now… the maths geniuses among us will probably notice there's not a huge difference between a number divided by 76 and one divided by 87. And you'd be right. 1 foot in 1:76 scale is approximately 4mm. In 1:87 scale it's 3.5mm, so not a massive difference at all. It only really comes into play hugely when you're using models that are exactly HO scale immediately next to OO scale.
So then… what about the trains?
OO scale locomotives, popularised by Hornby and other British model railway manufacturers since, were actually originally designed to run on HO scale track, which has a gauge or track spacing of 16.5mm between the rail centres. It was the most popular scale at the time so keeping the models compatible with existing ranges out there kept costs down but with a potentially massive market.
However, a problem arose with the sizing of the trains themselves. British locomotives tended to be smaller than their European counterparts and Hornby found that the bodies were too small to house the electric motors that were available at the time. The solution was to keep the width of the chassis correct to HO gauge but tweak the size of the bodies, making them slightly larger. Increasing the bodies to 1:76 scale (4mm to the foot) gave the engineers just enough room to house the motors, but the models remained compatible with the existing track systems.
Can OO scale trains run on HO scale track?
Yes! Because both scales use the same 16.5mm gauge track, OO scale trains will run perfectly well on HO scale track.
Furthermore, with most items of rolling stock being fitted with NEM pockets, it's possible actually run a mix of British and European rolling stock on the same layout, simply by swapping the couplings. This gives both British and European modellers access to a huge range of accessories, locomotives and rolling stock from a wide range of manufacturers.
Is OO gauge the same as HO?
Taking all of the above into account, there is no single definitive answer to this questions. In fact, there are two answers!
- In terms of locomotives & rolling stock compatibility, yes, OO gauge is the same as HO scale because they both run on exactly the same track.
- In terms of accuracy and realism when it comes to buildings and accessories, the answer is no, not really. Whilst you can mix and match the scales if you're careful, when you place a OO scale figure next to an HO scale one, you'll notice a difference in height of about 3.5mm between the two.
very entertaining and enlightening,thanks
In my model railway (HOe/OO9), I discovered that the Dapol Airfix) figures were clearly HO. When scratch-building, I use 1/80th, which seems a good compromise. My station building (OO) looks quite large.
I was fascinated to learn that OO was invented by Rovex Scale Models to accomodate larger motors!
It is hardly noticeable but can use perspective by putting smaller figures at back of scenery. Same with running a dock with HOm in front of N it becomes a layout with perspective. (I hope. Not finished yet).
James, Hornby Dublo predated Tri-ang Rovex by several years. I believe the Hornby Models were available Pre WWII but disappeared while the Binns Road Hornby factory converted to war work. Triang Rovex only appeared around 1950. My brother and I had one of the first Princess Elizabeth sets!
HO gauge is simply 16.5 mm. HO scale is defined in the USA in a set of standards written by the NMRA to ensure the interoperability of equipment produced by diverse manufacturers. I assume that continental Europe has similar standards under the NEM umbrella.
HO scale as described by NMRA standards, as far as track and wheels are concerned defines, amongst other things, wheelset back-to-back dimension, wheel tread profile and flangeway clearance.Most British models produced in the last 45 years appear to run satisfactorily on NMRA track, but I cannot guarantee other track. Old 'Steamroller' wheels probably will not.