For many people new to model railroading, the question of model train gauge versus model train scale can be quite confusing.  Here’s a simple explanation.  Gauge is the measurement of distance between the two outside rails of the track.  Model train gauges have been standardized to assist in easy identification of these specific dimensions.

Model train scale is simply the fractional equivalent for the gauge, and inches are used as the units of measurement.  For example, a model train designated as 1:48 scale dictates that 1″ of the model train equates to 48″ of the train it was modeled after.

Here’s a helpful chart:

Gauge Designation

Distance Between Rails

Scale

Standard

2.125″ (54mm)

1:24

G

1.75″ (45mm)

1:22.5 or 1:20.3

No. 1

1.75″ (45mm)

1:29 or 1:32

O*

1.25″ (32mm)*

1:48

Proto-48

1.169″ (43mm)

1:48

S

.875″ (22.5mm)

1:64

OO

.75″ (19mm)

1:76

HO

.650″ (16.5mm)

1:87.1

TT

.471″ (12mm)

1:120

N

.354″ (9mm)

1:160

Z

.256″ (6mm)

1:220

* O gauge measures the distance from the center of each of the two outside rails.

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