O scale model trains are all proportioned 1:48 to the prototype. In other words, they are 1/48th the size of a real train. O scale conveniently works out to 1/4 inch = 1 foot.
O is one of the oldest scales still in common use today. And it's popularity is growing. O scale can be confusing for beginners however because there are many variations.
2 vs. 3 Rails
Some O scale trains run on conventional two-rail tracks like other scales. The majority of mass-produced trains run on 3-rail track that is derived from a system developed by Lionel. The third rail simplifies wiring by making the outer rails the same polarity. This makes it possible to build reversing loops, wyes and turntables without a creating a short.
O scale track and curves don't follow all of the same conventions as other scales, read more about the different types of O scale track here.
Generally, two-rail O scalers are more apt to build a conventional scale layout with broad curves and scale equipment. 3-rail layouts have been generally thought of as more toy like. There is a quickly growing segment of the O scale market that is building highly realistic layouts using 3-rail track.
These "hi-rail" layouts combine the availability and generally lower cost of three rail models and track with a scale appearance. The term hi-rail comes from the oversized rails used in 3-rail track.
A large segment of the O scale market collects and operates trains that are more like toys than scale models. These trains date back to the 1940s and many are quite valuable. These layouts typically include very sharp radius curves and equipment that is reduced in size and modified to negotiate those curves. Simple tubular track and an abundance of animated accessories are also halmarks of a classic toy train layout.
Reproductions of many of the most popular trains and accessories from the past are still produced today along with more contemporary models. This makes it affordable for new-comers to recreate an operating layout, but can also be a challenge for new collectors who may think they are getting something old.
Even with their greater scale appearance, most two-rail O scale trains still suffer from one flaw...their gauge. The 1.25" standard gauge track used for most O scale models actually works out to 60 scale inches, slightly wider than the 56.5" of standard gauge. A small niche of the hobby actually corrects this by laying all track by hand and installing correct wheelsets on rollingstock.
Choosing O Scale
If you are considereing choosing O scale trains for your model rairoad, here are some thoughts to keep in mind.
- Availability - The most popular 3-rail O scale trains are widely available. Two-rail models are somewhat harder to come by, although 3-rail versions can be converted. For the collector market, older models can be found at train meets and online auctions. Obviously some are more plentiful than others.
- Cost - The cost of O scale trains varies greatly. 3-Rail trainsets are comparable in cost to smaller scales. More detailed scale models and collectibles can run very high prices.
- Size - The size of O scale trains makes them fairly easy to handle for children. The lighted and animated accessories and simple wiring of 3-rail track are also appealing. The overall size and mass of O scale models really captures the feeling of the prototype and offers a great platform for super-detailing and customizing models.
- Space - Toy train layouts, with their unprototypical curves, can actually be built in a rather tight area. A circle of O-27 track actually takes up less space than a comparable HO scale starter set with 18" radius curves. Scale layouts however will require a much greater minimum radius and necessitate a larger room for the layout. A 72" radius curve is considered adequate for most large O scale models - that means a simple circle will require a platform or room at least 12'x12'.