The British railway modelling page

(Last November 3rd, 2001)

1. The terms Scale and Gauge.

2. Drawings.

3. Terminology.

4. Gauges across the world.

The terms scale and gauge.

In the whole vocabulary of model railways there are no two more misunderstood and wrongly used words than "scale" and "gauge".

Essentially the word "scale" relates to the ratio in size between model and prototype, expressed as some form of direct comparison. It can be expressed as a fraction (e.g. 1/76th), a ratio (e.g. 1:76) or as a statement (e.g. 4mm equals 1ft). Regardless how it is expressed, its purpose is to convey an exact dimensional relationship.

"Gauge" is the word which relates to the distance between the running rails on the track itself. There are many different gauges to be found on the world's railways but they all fall into one of three categories: broad gauge (e.g. the 7ft gauge of the early GWR); standard gauge (e.g. the current 4ft 8 1/2ins gauge of British railways); and narrow gauge (e.g. the 1ft 11 1/2ins of the Ffestiniog Railway).

Taken separately, while not exactly simple, the two terms are at least unambiguous. It is when translating it into model terms that scale and gauge sometimes become intermixed or confusing. This is largely due to a couple of things: the habit of mixing imperial and metric units with a few ratios for good measure; and the different compromises that are often made through rounding up or down otherwise awkward measurements.

The following table will help clarify the situation as well as demonstrating why the confusion arises from time to time. It shows the commonly used types of models followed by the track gauge that is normally used for models of that type when depicting standard gauge track. Following this are the two commonly used methods of describing the scale and, in brackets, the prototype track gauge that it translates into. The majority of the examples of the scale/gauge combinations shown in this table are those commonly encountered by those modeling British railways. There are also examples for those modelling European and US railways, while the overall idea will interest any modeller.

Scales and Gauges
Type Track Gauge Ratio Gauge Scale Gauge
Z 6.5mm 220:1 (4'8 1/3") 1.4mm/ft (4'7 3/4")
N (Eur) 9.0mm 160:1 (4'8 3/4") 1.9mm/ft (4'7 1/2")
N (US) 9.0mm 160:1 (4'8 3/4") 1.9mm/ft (4'7 1/2")
2mm 9.42mm 152.4:1 (4'8 1/8") 2mm/ft (4'8 1/2")
OOO 9.5mm 152:1 (4'9") 2mm/ft (4'9")
N (UK) 9.0mm 148:1 (4'4 1/2") 2.06mm/ft (4'4")
TT (Eur) 12.0mm 120:1 (4'8 3/4") 2.54mm/ft (4'8 7/10")
TT (US) 12.0mm 120:1 (4'8 3/4") 2.54mm/ft (4'8 7/10")
TT (UK) 12.0mm 101:1 (3'11 3/4") 3mm/ft (4'0")
HO 16.5mm 87:1 (4'8 1/2") 3.5mm/ft (4'8 1/2")
OO (US) 19.0mm 76:1 (4'9") 4mm/ft (4'9")
P4 18.83mm 76:1 (4'8 2/5") 4mm/ft (4'8 1/2")
EM 18.2mm 76:1 (4'6 1/2") 4mm/ft (4'6 3/5")
OO (UK) 16.5mm 76:1 (4'1 1/2") 4mm/ft (4'1 1/2")
S 0.875" 64:1 (4'8") 3/16"/ft (4'8")
O (US) 1.25" 48:1 (5'0") 1/4"/ft (5'0")
O (UK) 32.0mm 43:1 (4'6 1/5") 7mm/ft (4'7")
S7 33.0mm 43:1 (4'8") 7mm/ft (4'8 1/2")
1 45.0mm 32:1 (4'8 3/4") 10mm/ft (4'6")
Note: The track gauge for EM was originally 18mm. However, the current standard is considered to be 18.2mm.

Several things become clear from the table. First, the track gauge rarely comes out the same when using the two conversion methods, which is a demonstration of the previously mentioned compromises. Second, regardless of the conversion method, the track gauge rarely comes out to exactly 4'8 1/2", though in most cases the results are very close indeed and the difference is not noticeable with the naked eye.

Finally, apparently identical types of models are not in fact identical. For example, models in N may run on the same track in the UK, Europe and North America and may be understood to be at a scale of 2mm/ft yet the ratio in the UK, which is used by the manufacturers, differs from that of Europe and North America. A second example is HO models and OO models which also both run on the same track but which are modelled to different ratios and correpondingly different scales. It helps explain why a UK model in OO and a North American model in HO have about the same loading gauge when in reality they are quite different with the North American loading gauge being considerable bigger. This is also why UK models in OO look as if they are running on narrow gauge track which they are if you look at the calculation; a scale 7" narrow! It is this narrow gauge look of OO that led to the development of, EM and P4, which are modelled to the same ratio and scale as OO but run on track which is closer to the correctly scaled down version.

Most of the foregoing focussed on standard gauge. For completeness, reference must be made to narrow gauge and broad gauge. Typically when one models a non-standard gauge prototype railway, one can indicate it by appending a suffix to the types described in the table. However, this too is not universal and there are at least two types of such suffixes.

In the UK and in North America, the suffix is made up of a lower case "n" followed by the prototype gauge expressed in feet. Thus, an Sn3 model railway models a prototype railway with rails 3 feet apart at a 1/64 scale.

In Europe, prototype gauges are placed in 4 categories: normal gauges (1.25 to 1.70 metre); metric gauges (0.85 to 1.25 metre); narrow gauges (0.65 to 0.85 metre), and industrial gauges (0.40 to 0.65 metre). Each non-normal category has its own suffix: "m" for metric; "e" for narrow; and "i" for industrial. Thus, H0m means a model of a prototype railway with a gauge between 0.85 and 1.25 meter at a 1/87 scale.

And you thought only computers were perverse!

Drawings.

Following the suggestion that a useful addition to the BRMNA web site would be an index of sources of drawings for those modelling British railways, four members were kind enough to provide the results of some indexing that they had been undertaking on their own behalf. Interestingly, the various categories suggested (locomotives, passenger stock, goods stock, trackplans, buildings and miscellaneous) closely matched the approach that they had taken. Moreover, the overlap was minimal. Following the creation of the initial version of the BRMNA index these same members plus others have provided additional material. Why not take a look? Even better, why not provide some addtional material?

In addition there is an independent index for those interested in the Southern Railway and its constituent companies.

Visit the Railway Station web site. This is an absolutely vast database which lists every published photo of UK stations and is the work of one man!

Terminology.

There are different terms to describe the same thing between the UK and North America. In addition there are terms that have no counter-part in North America. To reduce the confusion and increase your vocabulary check this out.

Gauges across the world.

As noted in the section on the relationship between gauge and scale, gauge is the distance between the running rails of the track. There are many different examples of gauges not only across the world but also within some countries as the following examples shows:

Gauges across the world
Country Track Gauge Track Gauge
(Imperial) (Metric)
Algeria1ft 11.6in0.600m
Algeria3ft 5.25in1.050m
Algeria3ft 3.75in1.000m
Algeria4ft 8.5in1.435m
Algeria4ft 9.2in1.45m
Angola3ft 6in1.067m
Argentina2ft 5.5in0.750m
Argentina3ft 3.75in1.000m
Argentina4ft 8.5in1.435m
Argentina5ft 6in1.676m
Australia3ft 6in1.067m
Australia4ft 8.5in1.435m
Australia5ft 3in1.600m
Belgium4ft 8.5in1.435m
Bolivia3ft 3.75in1.000m
Bulgaria1ft 11.6in0.600m
Bulgaria2ft 6in0.762m
Burma3ft 3.75in1.000m
Brazil3ft 3.75in1.000m
Brazil5ft 3in1.600m
Cambodia3ft 3.75in1.000m
Canada4ft 8.5in1.435m
Ceylon2ft 6in0.762m
Ceylon5ft 6in1.676m
Chile1ft 11.6in0.600m
Chile2ft 6in0.762m
Chile3ft 6in1.067m
Chile3ft 3.75in1.000m
Chile4ft 8.5in1.435m
Chile5ft 6in1.676m
China4ft 8.5in1.435m
Colombia3ft 0in0.914m
Colombia3ft 3.75in1.000m
Congo3ft 6in1.067m
Costa Rica3ft 6in1.067m
Cuba4ft 8.5in1.435m
East Africa3ft 3.75in1.000m
Ecuador2ft 5.5in0.750m
Ecuador3ft 3.75in1.000m
Ecuador3ft 6in1.067m
El Salvador3ft 0in0.914m
Ethiopia3ft 1.4in0.950m
Ethiopia3ft 3.75in1.000m
Finland4ft 8.5in1.435m
Finland5ft 0in1.524m
France4ft 8.8in1.44m
Germany4ft 8.5in1.435m
Ghana3ft 6in1.067m
Greece3ft 3.75in1.000m
Guatemala3ft 0in0.914m
Haiti3ft 6in1.067m
Holland4ft 8.5in1.435m
Honduras3ft 6in1.067m
India2ft 0in0.610m
India2ft 6in0.762m
India3ft 3.75in1.000m
India5ft 6in1.676m
Indonesia1ft 11.6in0.600m
Indonesia3ft 6in1.067m
Italy3ft 1.4in0.950m
Italy4ft 8.5in1.435m
Iran4ft 8.5in1.435m
Iraq3ft 3.75in1.000m
Iraq4ft 8.5in1.435m
Ireland3ft 0in0.914m
Ireland5ft 3in1.600m
Jamaica4ft 8.5in1.435m
Japan3ft 6in1.067m
Japan4ft 8.5in1.435m
Jordan3ft 5.25in1.050m
Korea4ft 8.5in1.435m
Lebanon4ft 8.5in1.435m
Malawi3ft 6in1.067m
Malaysia3ft 3.75in1.000m
Mauritius4ft 8.5in1.435m
Mexico3ft 0in0.914m
Mexico4ft 8.5in1.435m
Morocco4ft 8.5in1.435m
Mozambique3ft 6in1.067m
Newfoundland3ft 6in1.067m
New Zealand3ft 6in1.067m
Nicaragua3ft 6in1.067m
Nigeria2ft 6in0.762m
Pakistan2ft 6in0.762m
Pakistan3ft 3.75in1.000m
Pakistan5ft 6in1.676m
Panama3ft 0in0.914m
Panama5ft 0in1.524m
Paraguay3ft 3.75in1.000m
Paraguay4ft 8.5in1.435m
Peru3ft 0in0.914m
Peru4ft 8.5in1.435m
Philippines3ft 6in1.067m
Portugal3ft 3.75in1.000m
Portugal4ft 8.5in1.435m
Rhodesia3ft 6in1.067m
Saudi Arabia4ft 8.5in1.435m
Sierra Leone2ft 6in0.762m
South Africa2ft 0in0.610m
South Africa3ft 6in1.067m
Spain3ft 0in0.914m
Spain3ft 3.75in1.000m
Spain5ft 6in1.676m
Sudan3ft 6in1.067m
Surinam3ft 3.75in1.000m
Sweden2ft 11in0.891m
Sweden3ft 6in1.067m
Switzerland3ft 3.75in1.000m
Switzerland4ft 8.5in1.435m
Syria3ft 5.25in1.050m
Syria4ft 8.5in1.435m
Taiwan2ft 6in0.762m
Taiwan3ft 6in1.067m
Thailand3ft 3.75in1.000m
Trinidad4ft 8.5in1.435m
Tunisia4ft 8.8in1.44m
Turkey2ft 5.5in0.750m
Turkey4ft 8.5in1.435m
UAR2ft 5.5in0.750m
UAR3ft 3.75in1.000m
UAR4ft 8.5in1.435m
United Kingdom2ft 0in0.610m
United Kingdom2ft 6in0.762m
United Kingdom3ft 0in0.914m
United Kingdom4ft 8.5in1.435m
USA4ft 8.5in1.435m
USSR5ft 0in1.524m
Venezuela2ft 0in0.610m
Vietnam3ft 3.75in1.000m
West Africa3ft 3.75in1.000m
West Africa3ft 6in1.067m
Western Australia3ft 6in1.067m
Yugoslavia2ft 6in0.762m
Yugoslavia3ft 3.75in1.000m
Zambia3ft 6in1.067m

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