4ft 8½in. is by no means the only gauge in use – larger and smaller gauges are in regular use on different railways, and it is hardly surprising that modellers wish to replicate them or to use them as inspiration for their own ideas.

The table lists a wide range of prototype gauges. If a prototype gauge is modelled using a standard O gauge track, the scale varies. The smaller the prototype gauge, the larger the scale, and consequently the larger the locomotive and rolling stock models. The exact scales listed in the table are calculated assuming the O fine or O coarse track gauge of 32mm. If another standard is used (ScaleSeven O-MF or O-SF), the exact scales will differ slightly, but this is usually of little consequence because modellers often round the scale to a convenient number, shown in the table as a conventional scale.

If on the other hand a scale of 7mm/ft is used, the model gauge varies. Modellers are of course free to build track to any gauge that they choose, but for those who prefer not to or wish to save time, commercial track of the nearest available dimension may be used. This is shown as conventional gauge in the table. Many prototype gauges cannot be matched or can only be poorly matched in this way, and considerable compromise in the locomotive and rolling stock design must be accepted.

[1] 16mm/ft is a widely used scale with significant commercial backing, and is often used for this prototype gauge despite being technically too large.

[2] Known as BG7, and particularly used for modelling the GWR broad gauge.

The figures below, drawn to a consistent scale, show some of the scale and gauge combinations and their implications for the size of the models.

The Guild track and wheelset standards

The standards explained

Other track and wheel standards

This article was originally compiled by the Technical Committee for the Gauge O Guild Manual. It was updated and adapted for the GOGWiki by Nick Baines.