Model Railway Gauges | Scales

Rail gauge or scale is the distance between the inner sides of the two parallel rails that make up a railway track.

OO Gauge
4mm to 1ft, 1:76 scale
16.5mm gauge (inside track width)

A British system which is very well provided for, with a wide range of ready-to-run models, and accessories. This is the most popular gauge used by the railway model hobbist. However technically it suffers from the fact that the track gauge is 15% under scale (18.3mm would be the correct scale).

1 Gauge
10mm to 1ft, 1:30.5 scale
44.45 gauge (track width)

This is almost the biggest scale used for standard and narrow gauge modeling. Some enthusiasts prefer to use 3/8in to 1ft, which gives a more accurate scale/gauge ratio. These models would have to be scratch-built, although there are some very impressive, but expensive, ready-to-run models available in Continental Europe.

O Gauge
7mm to 1ft, 1:43.5 scale
32mm gauge (inside track width)

Once seen to be the preserve of those with the engineering skills to scratch build. This scale has become more popular due to the availability of a large range of quality locomotive and rolling stock kits. Technically the inside track width of 32mm is 3% under scale.

There has been a resurgence in “O” gauge, with a large numebr of kits on the market, and a number of manufacturers producing ready to run (RTR)locmotives and stock.

Scale Seven
7mm to 1ft, 1:43.5 scale
32.95mm gauge (inside track width)

A new refinement using exact wheel profiles and an exact scale/gauge ratio, hence giving greater accuracy.

S Gauge
4.76mm to 1ft, 1:64 scale
22.2mm gauge (track width)

A near perfect scale/gauge ratio, falling between 0 and 00. Little commercial support outside the USA means scratch building or adapting almost everything.

“S” gauge has become a little more popular recently, with articles in the modelling press, and a (limited)number of models, or parts thereof, becoming available.

EM Gauge
4mm to 1ft, 1:76 scale
18.2mm gauge (inside track width)

An attempt to make the 00 layout track gauge more realistic. At 18.2mm it still falls short of the ideal 18.83mm, but was felt by those involved to be near enough.

P4 Gauge
4mm to 1ft, 1:76 scale
18.83mm gauge (inside track width)

As EM is still slightly under scale, P4 was established. Locomotive and rolling stock kits are available with the option of an underframe plus wheels to fit this gauge.

HO Gauge
3.5mm to 1ft, 1:87 scale
16.5mm gauge (inside track width)

This is the major gauge used outside the UK. At 3.5mm to 1ft, the track gauge at 16.5mm is virtually exact to scale for the standard gauge. When using this gauge it must not be confused with 00 gauge, HO gauge is almost 15% smaller. One can run HO gauge rolling stock on 00 gauge layouts, the track gauges both being 16.5mm, but the difference in scale will be very obvious.

TT Gauge
3mm to 1ft, 1:101.6 scale
12mm gauge (inside track width)

This gauge originated in the USA, and was also produced at 2.5mm to 1ft, 1:120 scale. Enthusiasts using this scale need specialist support through the Three Millimetre Society.

N Gauge
2mm to 1ft, 1:148 scale in UK
9mm gauge (inside track width)

This gauge is half the size of 00 and therefore you should in theory be able to lay four times as much track. This is becoming a very popular gauge with a full range of locomotives, rolling stock and accessories. In Europe and North America the scale of 1:160 is used for N gauge models, running on 9mm gauge track.

2mm Scale
2mm to 1ft, 1:152.3 scale
9.42mm gauge (inside track width)

The purists of N gauge developed this scale. It is slightly more accurate than the mainstream scale of 1:148.

Z Gauge
1.5mm to 1ft, 1:200 scale
6.5mm gauge (inside track width)

This is a commercial gauge produced by Marklin. It is relatively expensive and specialist.

G Gauge
Scaled to suite modelled prototypes
45mm gauge (inside track width)

This gauge is used in garden layouts, with 2ft, 2ft 3in, 3ft and metre gauge models available.

SM32 Gauge
16mm to 1ft scale
32mm (0) gauge track.

Mainly the domain of scratch-builders, who have the engineering skills to produce live-steam locomotives.

0-16.5 Gauge7mm to 1ft, 1:43.5 scale
16.5mm gauge (inside track width)

A 00 track gauge for modelling rolling stock to be found on a 2ft 3in or 2ft 6in full size system.

OOn3 Gauge
4mm to 1ft, 1:76 scale
12mm gauge (inside track width)

Used for models of the Isle of Man railways and the Irish 3ft gauge systems.

H0m Gauge
3.5mm to 1ft, 1:87 scale
12mm gauge (inside track width)

Used for models of the Swiss metre gauge. Not quite to scale (11.5mm would be more accurate).

H0n3 Gauge
3.5mm to 1ft, 1:87 scale
10.5mm gauge (inside track width)

Used in the USA for modelling 3ft gauge prototypes.

H0-9 Gauge
4mm to 1ft, 1:76 scale
9mm gauge (inside track width)

Used by modellers that want to run 00 stock on N gauge track.

Posted in Tips and Advice.