An introduction to model railroading scales and gauges.

I am presenting this so people who are new to scale model railroading, or those that are interested, can eliminate some of the confusion between scale and gauge and the different scales out there.

To start things off we have what we call "Prototype". This is the real thing that rolls by at the station. Its scale is called 1:1 or 12 inch to the foot scale. It allows for the most super detailing, but most of us would be hard put to fit even one car into our backyards, let alone our "train room". In the US, and in many parts of the world, the distance between the insides of the railheads, or gauge, is 4'-8.5" (56.5") or "standard" gauge. Different parts of the world use different gauges, from Russia's 60" gauge down to a 15" gauge in Wales. Gauges larger than "standard" are known as "broad" or "wide" gauge and those narrower than standard are known as "narrow" gauge. In the US there were a mixture of different gauges on the mainline "Common carriers" until in the late 19th century when standard gauge was adopted for ease of interchange of cars. The widest in use was the Erie's 72" ( 6’-0”) gauge. A lot of narrow gauge railroads were built in the US, mostly, but not always, in the west. The East Broad Top is a 3' gauge railroad in Pennsylvania and Maine was famous for its 2' gauge railroads; the most notable being the Sandy River and Rangeley Lakes Railroad that had over 120 route miles of track. Sadly, it folded in 1935. The widest gauge of a common carrier railway, known to the author, was Isambard Kingdom Burnel’s (You have to love that name) Great Western Railway of Great Britain of 7’-01/4” or 2.14 meters.

Now that I have the real thing out of the way I will focus on the differences between scale and gauge. These terms are sometimes used interchangeably, but they are not. Scale refers to the proportion of the model to the real thing: H-O scale is 1/87 the size of the real thing. Gauge refers to the distance between the inside of the running rails: H-O gauge is 0.65". So there is no such thing as a H-O gauge person, unless that person is 56.5" tall, more correctly there are H-O scale people. If you are using H-O scale, but modelling a Maine 2 footer then the scale designation becomes H-On2. The "n" for narrow gauge and the "2" for the 2 feet between the rails. If you decided to model the old Erie then it would become H-Ow6, with the "w" meaning wide gauge.

I will list the most notable scale model railroading scales in descending order of track gauge.

First we have the "Live Steam" scales. These are the ones you can ride behind. The largest practicable live steam scale is 1/4 scale or 3" = 1'-0". The gauge for this is 14 1/8".
There are other scales, but they are normally referred to by their gauges: 7 1/2" gauge, 3" gauge, etc. There is a 15" gauge but that is mostly used in amusement park and is not considered a true model railroading gauge and more of an amusement ride. The scale of that gauge would be 1/3.766. You could use 3.75" to the foot and probably no one would notice the slight discrepancy

3 Gauge

An early 20^th century gauge of 2.5” between the rails giving a scale of 1:22.6 for standard gauge track. It is very close to 1:22.5 scale used to represent meter gauge track in G gauge.

2 Gauge

The second of the early 20^th century gauges, also known as II gauge. Originally 64 mm (2.52 in), but standardized in 1909 at 50.8 mm/2 in but since fallen into disuse. The gauge was introduced by Märklin at the Leipzig toy fair in 1891. 2 gauge was equivalent to 1:22,5 scale. 63 mm (2.48 in)/64 mm (2.52 in) gauge was standardised in 1909 as gauge 3. Gauge 2 was standardized at 2 in (50.8 mm).

"G" gauge

It has several different scales attached to it, though the track gauge, 45mm or 1.772", remains the same.
"G" gauge is occasionally referred to as the "Garden" gauge, because it is used in garden railways. The most prominent manufacturer of G gauge equipment is LGB, the originator of the gauge.
The scales that use G Gauge track are:
1:22.5 scale with the gauge representing meter or 3' 3 3/8" gauge track.
1:20.3 scale with 3' gauge track
1:24 scale - various manufacturers use this scale with its 42" gauge track which would be accurate for Newfoundland's trains.
1:29 scale with the gauge representing standard gauge track, though slightly narrow (51.388” vs 56.5”). It is interesting to note that 1/29th scale is three times larger than H-O scale, the most popular scale, at least in the U.S.

1 Gauge
The third of the early 20th century gauges that has not been seen in a long time. Scale was 1:32 and gauge was 1.75" or 44.45mm. Note that the gauge is very close to G gauge track.
1 gauge is still used but the models are re-gauged to use G gauge track.

O Scale/Gauge
A note must be made here. In the early days of model railroading the gauge was considered more important than the scale. This is the reason that the first 5 non-live steam items are considered gauges, not scales, though O, which was originally called 0 (zero), has made the transition to scale.
This scale has a varied history and a lot of confusion. In the early days, in England, the scale was 7mm to the foot and the gauge was 1.3". At one point the scale was changed to the easy to figure 1:48 or 1" = 4', though the gauge did not change. At some point the gauge got changed to today's 1.25". Some purists will insist that the scale for the 1.25" gauge is 9/32" = 1' - 0". Then you have the "Proto48"ers that maintain the 1:48 scale and change the gauge to a proper 1.177"

Lionel is the most famous of the manufacturers of O gauge equipment; using the 1:48 scale and 1.25" gauge.
Lionel's famous O27 is not a different scale or gauge. The "27" refers to the diameter of a circle of track. All O27 equipment can run on 1.25" gauge track, however the larger "O" equipment will probably not go around the tighter O27 curves. You must be warned Lionel’s O27 track has a different, or at least it did, height profile and O27 track and regular O track do not mate readily even though they are the same gauge.

S Scale
1:64 or 3/16" = 1' - 0". Gauge is 7/8" or .875".
Named for the scale of one Sixty-fourth scale, it was made popular by A. C. Gilbert's American Flyer line. This scale is used by a few die-hards and those that like the in between size of O and H-O. There are few manufacturers of S scale equipment today.

OO Scale
Known as Double O it is primarily an English scale and is 4mm to the foot or 1:76 scale and using H-O scale's .65" gauge.

H-O Scale
Probably the most used model railroad scale in the world. Named for being Half O scale it uses the scale of 3.5mm to the foot or 1:87.1. Its track gauge is .65".
This scale has the most equipment, and related items for any of the popular scales. For quick measuring of things; one inch in H-O equals seven feet three inches.
You will see this scale listed as either HO or H-O, as seen on this page. Both are correct, but I prefer the "H-O" as it is not an English language word and, I feel, it more properly represents what it stands for.

TT Scale
1:120 scale and a gauge of .471"
Named for being a Table Top size, it was scaled using an engineer's scale of 1/10" = 1'-0". This scale was uprooted by N scale. It is still popular in Eastern Europe, with Tillig a major manufacturer, though a couple years ago a European manufacturer tried to bring it back to the "Western world". I was recently informed that TT scale is making a comeback in the U.S. with some major manufacturers importing models.

N Scale
Two scales here now.
1:150 scale and 9mm gauge. Mostly used in Japan and in parts of Europe. It is a current alternate.
1:160 scale and 9mm gauge. This is the "classic" scale gauge combo for N scale.
Named for the gauge of Nine millimeters, it supplanted the long dormant TT scale and is approaching H-O scale in popularity and equipment selection.

OOO Scale
~1:160 scale and a gauge of 9 mm
Called Treble O it was introduced by Lone Star of London(?) in the early 1960s.
It lost its footing when Atlas Model Railroad Co. started importing N scale from continental Europe.

Z Scale
1:220 scale and 6.5 mm or 0.256" gauge
Z scale, or more properly "Zed" scale was first produced by Marklin in Germany. For years it was the smallest gauge and that is the reason it got its name.

T Scale
1:450 and a 3mm gauge
As in N scale it got its name from the gauge Three mm; it is currently the world's smallest true model railroading scale and is produced by a Japanese manufacturer. Yes, I have seen a set and have held them in my hand. The detail must be seen to be believed and the trains even have directional headlights and markers. A true marvel in smallness.

A non-scientific popularity of the smaller scales goes something like this: H-O, N, O, Z with the rest following. Note that this is a very subjective list and the NMRA probably has better data on the actual popularity of the various scales. However, there is no doubt of the top two spots.
As was mentioned OO is big in England and S scale is very limited, though you can still buy items for it. TT is probably a dead scale, except in Eastern Europe, as N scale filled the niche TT once had for being smaller than H-O. N scale is the same size as OOO and they can now be considered one, except for those few collectors out there that still have OOO equipment.

With O gauge being first called 0 (zero) gauge it was the smallest of the four numbered gauges back in the early days. The four being, from largest to smallest, 3, 2, 1, and 0. There is practically no 3 or 2 gauge equipment today, other than in collections. That being said, the three scales based on O/0 were originally known as 00, double zero; H0, half zero; and 000, treble zero. Over the years the way of saying zero changed to today's "oh" and the scales' names changed with the times.

If you any comments, suggestions or questions please e-mail me at lionkingcmsl@gmail.com

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