O Gauge vs. O-27 Gauge Model Railroad Track

What’s the difference between O gauge and O-27 gauge?

Before we explore different styles of track, a quick explanation of the difference between “O gauge” and “O-27 gauge”:

  • First of all, O-27 gauge track is the same gauge – or rail width – as O gauge track. All O gauge equipment will fit on O-27 track.*
  • Second, as you will see by the end of the next paragraph, “gauge” has nothing to do with “scale.”

Originally, O gauge track came in a minimum curve diameter of 31”, and O gauge trains were built (approximately) to a scale of 1/48 – that is, one inch of an O scale model was equal to 48 inches of the prototype of that model. Then along came the S gauge trains of American Flyer. Built to a smaller 1/64 scale that could negotiate tighter curves than O gauge trains, an S gauge layout took up less room than an O gauge layout, and marketers made much of this advantage.

In response, O gauge train manufacturers introduced O-27 gauge, which had the same rail width (gauge) as O gauge, but a minimum curve width of 27”. To make their O-27 trains able to negotiate these tight curves, they downsized the scale of the models (to about the same 1/64 used for S gauge models) to reduce their length.

The O-27 designation quickly became attached to Lionel’s “entry level” train sets, giving a status boost to their “standard” O gauge equipment.

Confused yet? Don’t worry too much, the difference between O gauge and O-27 is only important when it comes to old-school tubular track (we discuss track styles on our Choosing Track for an O Gauge Model Railroad Layout page), or if you have scale-length locomotives and train cars and try to use 27” curves. Nowadays, most manufacturers use the terms differentiate between scale of their models – referring to true 1/48 scale models as “O Gauge” and their smaller semi-scale models as “traditional” or “O-27 gauge.”

If you do opt for old-school Lionel tubular track, just remember, O-27 tubular track has a lower profile (rail height) than O gauge tubular track, and has brown metal “ties” while standard O gauge track is made with black “ties.” Old-timers will tell you that O gauge trains have deeper wheel flanges that don’t work on O-27 track, but I’ve never had a problem, and since all the newer track styles have rails the same or lower profile than O-27 tubular track, I doubt it’s an issue with any modern O gauge equipment.

*While “standard” O gauge trains will fit on O-27 track, because of their greater length, some may not be able to negotiate the tighter 27” curves.

Back to Choosing Track for an O Gauge Model Railroad Layout

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11 thoughts on “O Gauge vs. O-27 Gauge Model Railroad Track”

  1. At 69 I’m just getting into model railroading versus an old 1946 train which I watched go around and around with no switches till I would fall alsleep. I just inherited from my best buddy appx. 50 plus trains and who knows how many cars and buildings, etc.! Guess I’ll be going out in style. Just trying to learn everything I can before I start my first major project. That will be down the road (rail) once the estate is settled but I couldn’t have asked for a more memorable gift, along with everything else he left me (everything he owned). Should be a blast; one that people can usually only dream about!! Thanks ol’ buddy!

  2. Why can no one can tell me the length, width, height of O27, standard O, S, and O guage Lionel box and flat RR model train cars

    1. The length, width, and height of a boxcar will vary depending on the size of the prototype boxcar from which the model is made. Most full O gauge cars run about 12″ long, O27 cars usually about 9-11.” Height can vary but usually in the 3″ range.

  3. Very nicely done. I love the entire site. Will there be any more updates as I see it seems to be many years since last update.

  4. Newbie here, I just acquired an o-27 gauge layout, not paying attention I purchased a Conrail locomotive that will not negotiate the o-27 gauge curve. Is there anyway to substitute an O gauge curve into an o-27 gauge layout I have heard you cannot do this . Any help would be greatly appreciated.

    1. There are wider radius O27 gauge curves available that your locomotive could negotiate successfully. They are getting hard to find if you use tubular track, but there are many manufacturers that offer adapters to join their track to your O27 track. Lionel FasTrack is just one example that offers 36″, 48″, 60″, and 72″ curves.

  5. I want to run my 027 freight cars on AF 2 rail track. I know I’ll have to get AF engines, but is this the way to switch my set to 2 rail?

    1. If it’s O gauge track, you would need to find new trucks for your rolling stock that have insulated wheels, so you don’t short circuit electrical connection between the rails. If it’s AF S gauge track, you would need to get new trucks as well, as the gauge is narrower.

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