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Scale
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)
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.
References:
NMRA (National Model RR
Association)
Wikipedia
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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