Scale and Gauge

Definitions

Scale
The ratio between the size of the models and the size of the prototype. This can be expressed either as a ratio or as so many millimetres per foot (or fractions of an inch per foot for American models).
Gauge
The distance between the rails. Standard gauge is 1435mm (4 foot 8-1/2 inches) or the equivalent distance scaled down on the model. Anything narrower than this is called narrow gauge and anything wider is called broad gauge. In most cases the actual gauge used on the model varies slightly from the correct distance when scaled down from the prototype. Refer to the prototype gauge chart following for actual gauges used in various parts of the world.
Scale Name
Each popular scale is given a name which indicates, not only the scale to which the model railway / railroad model is being built, but also gives an indication of the track gauge used. The actual scale and gauge associated with a given name may vary depending on the prototype being modelled. In the case of narrow gauge the names also usually give an indication of the gauge of the prototype being modelled.

Prototype Gauge

The following chart is a representative list of some of the various gauges used by prototype railways around the world.

  Metric Imperial Countries/Regions
broad 2140mm 7′ 0-1/4″  Britain (GWR until 1892)
  1676mm 5′ 6″  Spain, Portugal, India, Chile
  1600mm 5′ 3″  Ireland (CIE, GNR, NCC), Australia (Vic, SA), Brazil
  1524mm 5′ 0″  Russia, Finland
standard 1435mm 4′ 8-1/2″  Australia, Austria, Belgium, Bolivia, Bulgaria, China, Czechoslovakia, Canada, Denmark, Egypt, France, Germany, Britain, Holland, Hungary, Italy, Japan, Yugoslavia, Mongolia, Norway, Poland, Peru, Rumania, Sweden, Switzerland, Turkey, USA
narrow 1067mm 3′ 6″  Australia (WA, SA, Qld, NT, Tas), New Zealand, South Africa, Japan, Spain, East Africa, Canada (CNR, Newfoundland), Ecuador, Java
  1000mm 3′ 3-3/8″  Germany, Switzerland, Spain, India, Burma, Kenya, Malaysia, Thailand, Uganda, Chile
  950mm 3′ 1-1/2″  Italy (Dolomites, Sardinia)
  914mm 3′ 0″  Isle of Man, Ireland (County Donegal), USA (D&RGW), Canada (WP&Y)
  800mm 2′ 7-1/2″  Wales (Snowdon Mtn Rly), Switzerland (Wengernalp Rly)
  760mm 2′ 6″  Australia (Vic), Wales (Welshpool&Llanfair), Austria (Zillertalbahn), India
  750mm 2′ 5-1/2″  Germany, Egypt, Indonesia
  686mm 2′ 3″  Wales (Tal y Llyn Rly)
  610mm 2′ 0″  Australia (Qld, Tas), Fiji
  600mm 1′ 11-5/8″  Wales (Festiniog, Vale of Rheidol), Greece
  381mm 1′ 3″  Romney Hythe & Dymchurch and Ravenglass & Eskdale (UK), Driving Creek (NZ)

Standard Gauge

The following are some of the scales that are (or have been) used by modellers to model standard gauge railways. The gauges used vary in the accuracy of their representation of true standard gauge. The more common and popular scales are shown in bold.

Name Scale mm/ft gauge (mm)  
4 1:15 4/5in 3in  
3 1:18 2/3in 2-1/2in  
2 1:24 1/2in 2in  
1 1:30.5 10 45  British
1 1:32 9.5 45  European
1 1:32 3/8in 1-3/4in  American
O 1:43.5 7 32  
Scale 7 1:43.5 7 33  
O 1:45 6.8 32  European
O17 1:45 17/64in 1-1/4in  American
O 1:48 1/4in 1-1/4in  American
Q 1:48 1/4in 1-3/16in  American
Proto 48 1:48 1/4in 29.89  American
S or H1 1:64 3/16in 7/8in  
OO 1:76.2 4 19  American
P4/S4 1:76.2 4 18.83  
EEM 1:76.2 4 18.8  
EMF 1:76.2 4 18.2  
EM 1:76.2 4 18  
OO 1:76.2 4 16.5  British
HO 1:87.1 3.5 16.5  
QO 1:96 1/8in 3/5in  
TT 1:100 3 13  European
TT3 1:101.6 3 12  British
Scale 3 1:102 3 14.12  
TT 1:120 2.54 12  
HOO 1:145 2 10  
N 1:148 2-1/16 9  British
OOO 1:152 2 9.5  
N 1:160 1.9 9  
K 1:174 1.75 8  
QOO 1:174 1.75 7.62  
Z 1:220 1.4 6.5  
X 1:304.8 1 4.5  
T 1:450 0.68 3  

Narrow Gauge

The following are some of the scales that are (or have been) used by modellers to model narrow gauge railways. The more common and popular scales are shown in bold.

Name Scale mm/ft gauge (mm) gauge prototype  
SM45 1:19 16 45    approx. 3 on 1 track
SM32 1:19 16 32 two foot  approx. 3 on O track
2n3 1:24 13 45    
2m 1:22.5 13.7 45 metre  
G 1:22 14 45 metre  LGB – approx. 2 on O track
G 1:29 14 45    (some models)
Gn15 1:22 14 16.5 15 inch  
Om 1:48 7 22.5 metre  
On3 1:48 1/4in 19 three foot  O on American OO track
On2-1/2 or On30 1:48 1/4in 16.5 two foot six  O on OO track
Oe 1:48 1/4in 16.5 750mm  O on OO track
O16.5 1:43.5 7 16.5 two foot  O on OO track
On2 1:48 7 14 two foot  
Sn3-1/2 1:64 3/16in 16.5 three foot six  
Sn3 1:64 3/16in 14 three foot  
Sn2 1:64 3/16in 9 two foot  
OOn3 or OO12 1:76.2 4 12 three foot  OO on TT3 track
OO9 1:76.2 4 9    British OO on N track
OO6 1:76.2 4 6 eighteen inch  British OO on Z track
HOm 1:87.1 3.5 12 metre  HO on TT track
HOn3 1:87.1 3.5 10.5 three foot  
HOe 1:87.1 3.5 9 750mm  
HOn2-1/2 or HO30 1:87.1 3.5 9 two foot six  HO on N track
HOn2 1:87.1 3.5 6 two foot  HO on Z track
TTn3 1:101.1 3 9 three foot  TT3 on N track
Nm or Nn3 1:160 1.9 6.5    N on Z track
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