Model Railway Gauge and Scale Guide

It is important to understand the difference between gauge and scale. Like real-world railways, the
gauge is the distance between the rails, with trains and rolling stock built for each particular
gauge; scale is the proportion that the size of the model is compared to its real-world equivalent.
The scale is normally expressed as a ratio (1:16 or 1/16) or a size (1 inch :1 foot). Sounds simple
enough? Not quite!

When a model train is scaled down the gauge is not necessarily to scale, but to
the nearest standard gauge. This means that you could have two different trains, both with the same
gauge, but a slightly different scale. In practice, this will be hardly noticeable, but it is worth
bearing mind.

In decreasing order of size, the most common model railway gauges are:

G Gauge
Variable scale
45mm gauge

O Gauge
7mm to 1ft, 1:43.5 scale
32mm gauge

OO Gauge
4mm to 1 ft, 1:76 scale
16.5mm gauge
OO is by far the most popular gauge, although the gauge is 15% under scale.

HO Gauge
3.5mm to 1ft, 1:87 scale
16.5mm gauge
The same gauge as OO, but with the smaller scale the gauge is in correct proportion to the scale.

N Gauge
2mm to 1ft, 1:148 scale
9mm gauge
Twice as small as OO gauge