Summary of Railroad Scales




Name of Scale Scale to Foot Proportion Coupler Center Above Railhead Track Gage Remarks
1" 1.000" (25.4mm) 1:12 2 7/8" (73mm) 4.750" (121mm)
3/4" .750(19.Omm) 1:16 2 1/4"(57mm) 3.500"(88.9mm)
17/32" .531"(13.5mm) 1:22.6 l 7/16"(37mm) 2.500"(63.5mm)
1/2" .500"(12.7mm) 1:24 1 7/16"(37mm) 2.500"(63.5mm)
3/8 .375"(9.52mm) 1:32 1 1/16"(27mm) 1.766"(44.9mm)
O(17) .266"(6.75mm) 1:45.2 11/16"(17mm) 1.250"(31.8mm) ++
O .250"(6.35mm) 1:48 11/16"(17mm) 1.250"(31.8mm) ++
On3 .250"(6.35mm) 1:48 9/16"(14mm) .750"(19.0mm)
On2 .250"(6.35mm) 1:48 11/32"(8.7mm) .500"(12.7mm)
S .188"(4.76mm) 1:64 17/32"(13mm) .875"(22.2mm)
Sn3 .188"(4.76mm) 1:64 17/32"(10mm) .563"(14.3mm)
OO 4.0mm(.1575") 1:76.2 29/64"(12mm) .750"(19.0mm)
HO 3.5mm(.1378") 1:87.1 25/64"(9.9mm) .649"(16.5mm)
HOn3 3.5mm(.1378") 1:87.1 9/32"(7.1mm) .413"(10.5mm)
HOn2 3.5mm(.1378") 1:87.1 .276"(7.01mm)
TT .100"(2.54mm) 1:120 9/32"(7.1mm) .471"(12.0mm)
TTn3 .100"(2.54mm) 1:120 7/32"(5.54mm) .300"(7.62mm)
N .075"(1.90mm) 1:160 .216"(5.5mm) .353"(8.97mm)
Nn3(40") .075"(1.90mm) 1:160 .250"(6.35mm)
Z.055"(1.39mm) 1:220 .257"(6.52mm)

++ Except for track gage and associated dimensions, STANDARDS for these scales are generally the same and are referred to simply as "O" STANDARDS.