HO, HOn3, HOn30 SCALES MODEL RAILROAD ( TRAINS

HO Scale 1:87.1, Gauge: 0.649” (16.5mm) The most popular scale worldwide scale. In North America, the space between the rails of a real-life railroad track is 4 feet 8 inches (1,422.4 mm). HO trains is (1/87) so you would calculate standard gauge in HO scale by dividing 1,422.4mm by 87.1. your result, 16.33mm, is very close to the 16.5mm adopted by model railroad manufacturers as HO gauge. This page lists the scales and gauges standardized by the National Model Railroad Association for modeling HO standard gauge railroad. In real-life railroading there were also narrow gauges; 3 feet being common in the United States