Reference

Australian Model Railway Association Incorporated

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
	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 Lyn Rly)
	610mm	2' 0"	Australia (Qld, Tas), Fiji
	600mm	1' 11-5/8"	Wales (Festiniog, Vale of Rheidol), Greece

 

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.

Scale Name	Ratio	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
X	1:304.8	1	4.5

 

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.

Scale Name	Ratio	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)
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		N on Z track