Scales & More

Modeling Scales

Scale & Gauge

As you get into deciding just what you want in the way of a model railroad, the question of scale comes up. Do you want HO or N or maybe O or S? Perhaps you want one of the Garden Railroad scales or gauge or... Well, what is scale and gauge for that matter? Briefly, scale is the ratio of the model to the real thing or 'prototype'. Gauge is the distance between the rails unless you are thinking 'Tinplate' or 'Scaleplate' like Lionel®, Marx®, American Flyer® or MTH® among others. Confused? Ah, well, let's look at scale first.

Scale implies that is it a scaled down version of the real thing. O scale used to be called 1/4 inch scale with the ratio to the real thing as 1:48 with HO being 1/8 inch scale and 1:86 or 1:87. That makes it simple except that there have been some subtle changes in HO and it is now 3.5 mm and 1:87.1. How about N scale? It is 1:160. Let's just look at size. O is the larger of the traditional scales. Lionel is O27 for example and is not truly O scale. S is smaller than O and came from American Flyer. HO is the next size and has been referred to as Half O with N scale being about half of that. And then there is Z. Z is small, really, really smaaallll at 1:220.

The following photo will give a good visual comparison between two of the scales - O and HO.  As you can see from above, HO scale is about half of O scale.  In fact, it is said that historically, the name "HO" was insipired by it being "Half O".  Even though every linear measurement in O scale is about twice the same measurement in HO scale, remember that each measurement in a 3-D item in O scale is twice that in HO scale. (i.e. length, width, height)  So, for example, the volume of a structure in O scale is actually eight (8) times that of the same structure in HO scale.  That is an important factor to remember when considering space requirements for each scale.  The structures in this photo are virtually the same, only one is built in O scale and the other in HO scale.  Thanks to George Downer of the Tidewater Division for both the photo and for building the structures!

In both HO and N scales, there is a large selection of quality products available with S scale growing rapidly. The selection of scales is up to the modeler. With N scale, you can have those long trains like the prototype runs through landscape that actually dwarfs the trains if that is what you wish. HO is said to be a better operating scale that allows almost trouble free switching for those way freights, locals and yard switching operations. In fact, there can be layouts that do all of these things in any of the major scales. The larger the scale, the more room it takes for an extensive layout. The question of scale depends somewhat on what you want your railroad to do. One thing I feel that I should mention at this point is that you cannot have twice the N scale railroad on a 4x8' as an HO. They do not scale out exactly and both have requirements that make you design the railroad to fit the space rather than using the other scale's track plan exactly. I have not mentioned OO and TT. They are minority scales in the U.S. but each has their advocates.

Well, then, how about gauge? Gauge is the distance between the tracks. Normal track gauge is 4' 8 1/2" between the rails. Using HO as an example, HOn3 means HO scale, narrow gauge, 3' between the rails. HOn2 would be HO scale, narrow gauge, 2' between the rails. HOn30 is a little different as that is HO scale, narrow gauge, 30 inches between the rails.

This photo shows some dual guage track in HO and HOn3 with a  standard HO scale truck and an HOn3 truck on the tracks for comparison.

S scale narrow gauge is growing because you can put a nice size narrow gauge layout into a space not much bigger than a modest HO layout. With the release of Bachmann's On30 train set, a number of modelers have jumped on it as they can have O scale people and buildings with smaller trains that run on track about the size of HO. As you get older, you sometimes appreciate larger cars and buildings. And of course if you really want larger cars, people and buildings, you can take a look at the various Garden Gauge scales.

For more technical information about scales and proportions, you can read Standard S-1 Overview. S-1 is a part of the NMRA Standards that help determine the ability of your cars and locomotives to interchange with other modelers' cars and locomotives in the same scale. Below I list some of the common scale's scale and proportion.

O(17) .266" (6.75mm) 1:45.2
O,On3,On2 .250" (6.35mm) 1:48
S,Sn3 .188" (4.76mm) 1:64
OO 4.0mm (.1575") 1:76.2
HO,HOn3,HOn2 3.5mm (.1378") 1:87.1
TT, TTn3 .100" (2.54mm) 1:120
N, Nn3 .075" (1.90mm) 1:160
Z .055" (1.39mm) 1:220

You will hear terms like Proto87 and 'Finescale'. They are very much a part of the scale that they refer to, but reference differences in track and wheel standards and practices. They have very little effect on most beginners and will be mentioned again later.

Lastly, we return to O27 gauge trains. The trains that we commonly refer to as 'Tinplate', 'Hi-Rail' or 'Scaleplate' run on track that doesn't scale out to the real thing for the size of the trains. Many times, the train cars and locomotives are shortened versions of scale. There is nothing wrong with building a layout around this equipment and there are a large number of layouts around the country using 3-rail track and 'Tinplate' or 'Scaleplate' type of equipment. They are model railroads. They are just not 'scale' model railroads in the same way that HO and N are.

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Page last updated December 2, 2014