To a newcomer, and even many people with years of experience, the phrase “On30” is confusing. Basically, it’s O scale models (1:48) of narrow-gauge (30 inches in this case) railroads.

And that probably raises a few more questions, so I’ll try to answer them.

## What is narrow gauge?

This is an On30 layout. The trains and track are smaller than what you see on more common large trains such as those run by Union Pacific, BNSF, NOrfolk Southern, CSX, or Kansas City Southern. Photo credit: Zabdiel/Flickr

Standard railroad track in the United States and many other parts of the world is 4 feet, 8.5 inches wide. There’s an Internet meme out there about why that measurement was chosen and it involves the wrong end of a horse, but it’s widely discredited.

And under normal circumstances, that gauge works pretty well. But under some conditions, such as short runs or mountains, a narrower gauge can make sense.

## Why is it popular to model?

Narrow gauge lines tend to be much smaller than main lines. So to a modeler who craves accuracy, narrow gauge is attractive. It’s not possible to build a scale model of the Union Pacific. It is possible to build a scale model of a small narrow gauge line serving a specific industry, and then you can include every single detail, if desired.
Consider this: I have an 8×8 layout in my basement. My wife thinks it’s enormous. But, in O scale, that’s an area of 384 feet by 384 feet. That’s a city block, roughly. There is no reason in the real world for the Union Pacific to be running two trains in circles inside a city block.

That bothers some hobbyists but not others. For a hobbyist with limited space who wants to make a layout that looks more believable, narrow gauge is a good option.

Two other things drive On30. It uses the same track gauge as the popular HO scale, as the width of HO track works out to 32 inches in O scale–close enough for most people. So, as HO scale modelers age and want something a little bit bigger, it’s possible to just replace the buildings on an HO scale layout and convert it to On30.

And On30 is marketed toward the holiday village crowd (think Dept. 56 or Lemax), making it a borderline mass-market item. Or certainly more mass market than most other O scale/gauge items. Whether it’s because of the dual markets, or certain parts commonality with HO scale, the pricing on On30 is lower than what we usually associate with brands like Lionel.

## I know O scale when I see it. Why are On30 models so small?

On30 cars are smaller than their regular O scale counterparts because real narrow gauge cars were smaller than standard gauge cars. Running full-size mainline cars on the short and/or mountainous runs on real-world narrow gauge railroads is impractical.

## So what are On2 and On3 and On18?

These are simply O scale representations of other widths of narrow gauge track. On2 is 2 feet wide, On3 is 3 feet wide, and On18 is 18 inches wide.

30-inch track is actually rare in the real world, so some hobbyists re-gauge On30 models to On2 or On3. On30 is much more common commercially, even though in the real world, 2- and 3-foot gauge was more common. The reason, of course, is because On30 shares so much in the way of parts commonality with HO scale. As with many other things, price wins out over realism.