This page provides some introductory information about the sizes of model trains, specifically about scale and gauge, the two most important terms in understanding a model train and its relationship to a prototype (the real thing).
The scale is expressed as a ratio, for example, 1:87, for HO scale. This means that an HO scale model is 1/87th as large as its prototype.
Gauge (Track Size)
The other important measure in model railroading is gauge. The term gauge refers to the size of the track on which the model trains operate. The gauge is a measure of the distance between the rails. Another measurement term you may hear with respect to track is code. Code refers to the height of the rail. A couple of general recommendations if you're planning a layout: stay with one type of track system if possible (your life will probably be easier), and, use the widest curves you have room for. Wider curves allow for smoother running and longer cars.
G is the largest of the popular scales. At First Hobby, we refer to several scales collectively as G scale. We lump together scales from 1:20.3 through 1:32 as G. That includes scales such as 1:22.5, 1:24 and 1:29. We identify the specific scale for G items in our descriptions of the items when it's known, but manufacturers don't always provide this information. Items with different G scales may work fine together--much depends on how it looks to you. The most likely problem you will have in mixing and matching products from different manufacturers is coupler mismatches. Fortunately, there are solutions available; we can help if you have questions about this. G scale is also known as the Garden scale, as these trains are frequently operated outdoors. Because of this, almost all G scale products are rated for use either indoors or out. We carry most of the popular names in G scale, including LGB, Aristo-Craft, USA Trains and Bachmann.
All of the G scale products we carry, and most of those sold in the United States, run on the same gauge of track, usually referred to as #1 gauge (about 1.75" between the rails). So, any of the trains can run on just about any of the track. However, mixing track from different manufacturers may be difficult as the track varies in construction and joining techniques.
O scale is 1:48, roughly half the size of G scale. You will also see some items described as O-27. O-27 locomotives and cars are usually a bit shorter than true O scale. Many train sets, especially starter sets are O-27. O and O-27 products can normally be mixed together without problems. Most O scale manufacturers have both O-27 and O products. First Hobby carries many of the popular lines in O scale, including Lionel, MTH and K-Line, along with many others. O scale trains can be a good size to match up with many of the porcelain village collections available today.
O gauge track is about 1.25" between the rails. This is the same of either O or O-27 track; O rails are usually taller than O-27 rails though. One difference you'll notice about most of the commonly available O gauge track is that it has 3 rails--2 outside rails and a center rail; this is different from G, HO or N track. Most O scale equipment uses the 3-rail track system; the center rail is used to provide power to the trains. There are 2-rail O scale products, but they are less common. O and O-27 track, or track from different manufacturers, can usually be joined, but again, working with a single track type is usually easier.
In our O Scale department you will also see a category called On30 Train Sets. The On30 products we carry are from Bachmann. The locomotives and cars are O scale, but the track used is HO gauge, so these trains can't be mixed in with either O or HO trains.
HO scale is 1:87, close to 1/2 the size of O scale. HO scale has the largest variety of products and manufacturers. First Hobby carries most of the leading HO manufacturers' products, including Atlas, Athearn, Life-Like, Bachmann, Model Power, Rivarossi, IHC and Walthers.
HO gauge track has rails a bit over 5/8" apart. All of the HO locomotives and rolling stock we sell use the same HO gauge track, but, as with other gauges, mixing different track systems can be challenging.
N scale is the smallest of the 4 most popular scales. N is 1:160, a little over half the size of HO. The advantage to the smaller sizes, HO, and especially N, is that more territory can be modeled in a smaller space. First Hobby carries N scale products from Kato, Micro-Trains, Con-Cor and others.
N gauge track has the rails just under 3/8" apart.