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Model RR Scales

Model RR Scales

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refers to the relationship between the size of the model and the size of the real railroad equivalent.  It is expressed as a ratio (e.g., 1:87) meaning the model is 1/87th the size of the actual railroad part or as a measurement (e.g., 1/8" = 1') meaning 1/8th of an inch on the model equals one foot on the actual railroad part.  These measurements are somewhat approximate but are adequate for our purposes.  See the references for more detailed information.

Gauge is the distance between the rails.  The standard gauge in the United States and much of the rest of the world is 4' 8 1/2".  A gauge smaller than standard is called narrow gauge and one larger than standard is called broad or wide gauge.  Only standard gauge is discussed here.

(Most popular scales in bold - O, HO, N are almost x2 difference)

G Scale: (1:20.3)
(Actually, 3' narrow gauge in US modeling practice)
O Scale: (1:48 or 1/4" = 1')
S scale: (1:64 or 3/16" = 1")
HO Scale: (1:87 or 1/8" = 1')
TT Scale (1:120 or 1" = 10')
N Scale: (1:160)
Z Scale: (1:220)

See Photo 1 ReferenceSee Photo 2 Reference

An added complexity is that a particular model railroad track gauge can be considered for use in a scale where it represents a track gauge other than 4' 8 1/2".  For example G gauge track is used to represent everything from narrow gauge to standard gauge.  HO track is used to represent O scale narrow gauge (On30).  Doing this lets modelers take advantage of availability of standard track components.

So called live steam model railroads are the ones large enough for people to ride.  They range in size from the ones found in zoos with gauges ranging from 15" down to 5" and less.  They are not discussed further here.

NMRA (National Model RR Association)
Model RR Scale Comparison 1 (Photo)
Model RR Scale Comparison 2 (Photo)
Model Train Scales
Model RR Life Size Scale Calculator

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