When planning on making a model railway, first you need to decide what scale you're going to work in. This will likely be decided on the basis of your funds and space to work in, although occasionally, a model of a certain class of locomotive or a particularly good rendition of a building can be the inspiration for working in a set scale.

Most models are electrically powered, although in larger scales, models of steam locomotives can be powered by 'live steam', coal - boiling water and driving wheels via pistons and connecting rods. Although it is possible to buy 00 gauge live steam models of classic steam locomotives, the cost of such a loco is beyond most modellers' pockets; extra equipment is needed in addition to the locomotive.

Diesel locomotives powered by internal diesel engines are also available in the larger gauges.

Scale

A model railway's scale is the model's size when compared to the full-sized engine. Although most model railways are based on standard gauge layouts, modelling narrow-gauge railways is becoming increasingly popular. For instance, on a 00 Gauge track, if you use the track as a standard gauge railway, your layout is modelled on the principle that the gap between the rails is 4 feet 8½ inches (1435mm), and everything on your railway would be exactly a seventy-sixth of the real size. However, if you use the same track as a narrow-gauge railway, you can model on the principle that the same gap is, for instance, now 2 foot, and subsequently run much larger models on the same size track.

Gauge

The gauge is the inner distance between the two rails, from inner head to inner head¹. British standard gauge is 4 feet 8½ inches (1435mm), a measurement based on the traditional width of a horse-drawn wagon and required by law by the 1846 Railway Regulation (Gauge) Act.

A brief list of the major popular gauges for railway modelling are:

• G Gauge - 16mm = 1 foot scale (1:19)
  
  Short for Groß, meaning Large, G gauge is also known as Garden Gauge as due to its large size is impractical for most indoor spaces and normally used outside on Garden Railways.

• Gauge 3 – 13.5mm = 1 foot scale (1:22)
  
  Also known as 3 Gauge, one of the original scales, largely replaced by G Gauge.

• Gauge 1 - 10mm = 1 foot scale (1:30)
  
  Gauge One, this was the dominant railway size worldwide before the Second World War, but has declined in popularity as smaller railways have become available. Gauge 2 at 1:29 was only marginally larger, and consequently was overlooked in favour of Gauges 1 and 3.

• 0 Gauge - 7mm = 1 foot scale (1:43)
  
  Gauge Zero. Another formerly extremely popular modelling scale in the early days of model railways that has declined in popularity over the last 60 years as smaller railways have increased in availability.

• S scale - 4.7mm = 1 foot scale (1:64)
  
  A Sixty-fourth the size of a full size engine.

• 00 Gauge - 4mm = 1 foot scale (1:76)
  
  Double-O gauge is by far the most common model railway size in Britain.

• EM Gauge - 4mm = 1 foot scale (1:76)
  
  EM (Eighteen Millimetre gauge, at 4mm to the foot, is actually 18.2mm if you want to be really picky. When introduced, the decision was made to keep to 4mm scale so that 'ready to run' models for the British standard 00 gauge could be easily adapted through merely re-wheeling.

• P4 gauge - 4mm = 1 foot scale (1:76)
  
  P4 (Proto4) As EM gauge only represents 4'7" gauge, so protofour gauge was developed. This has a gauge of 18.83mm, which works out as EXACTLY four feet eight-and-a-half, which is Standard gauge for full-sized trains.

• H0 gauge - 3.5mm = 1 foot scale (1:87)
  
  Half 0. It can run on the same track as 00 Gauge, but is slightly smaller.

• TT gauge - 3mm = 1 foot scale (1:100)
  
  TT (Table Top) was originally, as its name suggests, designed to cater for layouts on tables. Though smaller than 00 it is often just as detailed, allowing for ambitious layouts in restricted spaces.

• N gauge - 2mm = 1 foot scale (1:148 'British N', 1:150 in Japan, 1:160 elsewhere)
  Short for Nine mm, this is the world's most popular small-scale railway.

• Z gauge - 1.4mm = 1 foot scale (1:220)
  
  Z gauge is the domain of one ready-to-run² model manufacturer, Märklin, who produce continental European models.

• T gauge – 0.7mm = 1 foot scale (1:480)
  
  The smallest model train scale available at time of writing.

Since model railways were first introduced, two trends have affected model railway scales and gauges. Model railways have become increasingly accurate. They have also become smaller as the technology to make smaller and smaller railways have developed. One side effect of this is that large traditional scales in which models have been built, including gauges 2 and 3, are no longer as popular as they once were.

'L Gauge'

'L-gauge' is often used to describe model trains built of Lego, running on standard Lego track. Consequently, the techniques used in modelling in L gauge are different from those used in any other scale.

OO Gauge

If you are just starting out in the world of model railway building in Britain, it is recommended that you start in the dominant and widespread 00, pronounced 'double-o', scale. The widest range of models and kits are available in this size, which is generally considered a pleasing scale to work with. It is not too fiddly, not horrendously expensive and easy to collect a wide range of rolling stock and scenery for, as all major model railway manufacturers construct railways in this size. Decent layouts can be set up even for railway modellers with restricted space. Another reason for this scale's dominance is that it was created in 1921 by German toymaker Bing and has been the standard size for Britain's dominant model railway manufacturer, Hornby, since 1938.

H0 Gauge

H0 scale is the global standard for model sizes between 0 and N scale, but it is almost unknown in the UK where 00 gauge dominates, except for models of foreign locations and rolling stock. HO is slightly smaller than OO.