This article is from the Model Trains FAQ, by Christopher D Coleman with numerous contributions by others.
Scale is the relation or ratio of sizes between a model and a
prototype. For X:Y a dimension of X units on thesmodel
corresponds to Y units on the prototype. For example, if a real
boxcar is 500" long and you want yoursmodel in 1:100 scale, then
the model should be 100 times smaller, 500"/100, or 5"
long. Conversely if yoursmodel boy is 1" tall and in 1:50 scale,
then if he were real he would be 1"X50 or 50" tall. Over the
years manysscales have been defined, but the primary ones
collected are:
II (two) 1:22.5
Standard/Wide: none defined but would be about 1:27
G [see below] 1:24
I (one) 1:32 (1:29 for Aristo-Craft)
O (oh or zero) 1:48 in North America
1:45 or 1:43.5 Europe
S 1:64
Standard: 2-1/8"
Wide: 2"
G 45mm (1.77")
O std 1-1/4"
S std 7/8"
 
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