Scale and Gauges
Scale:                  Proportion:                    Track Guage:
G                      1:22.5, 1:29, 1:32              1.75"
O                               1:48                          1.25"
S                                1:64                          0.875"
HO                            1:87                          0.650"
TT                             1:100                        0.471"
N                               1:160                        0.354"
Z                               1:220                         0.256"
Gauge:
The distance measured inside the rails
This information is provided by the Model Railroad Industry Association, Inc