S Scale is the common name for modeling at 1:64 or 3/16″ to the foot. Railroad modeling in S Scale is principally divided into standard and narrow gauge modeling. Standard gauge modelers represent a real world track gauge of 4′ 81/2″ using a track gauge of 22.42 mm or 0.883 of an inch. Narrow gauge modelers typically fall into three classes: Sn42 representing a real world 42″ track gauge at 16.5 mm or 0.650 of an inch, Sn3 representing a real world 3′ track gauge at 14.3 mm or 0.563 of an inch and Sn2 representing and real world track gauge of 2′ at 10.5 mm or 0.413 of an inch (the same as HOn3 gauge track.)
The standards or recommended practices for modeling in S have been uniformly set and adopted by both the National Association of Model Railroaders (NMRA) and National Association of S Gaugers (NASG). Complete standards are also available from the S Scale SIG on this site.