- 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).
- 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.
The following chart is a representative list of some of the various gauges used by prototype railways around the world.
|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)|
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.
|S or H1||1:64||3/16in||7/8in|
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|
|G||1:22||14||45||metre||LGB – approx. 2 on O track|
|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|
|Sn3-1/2||1:64||3/16in||16.5||three foot six|
|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|
|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|