HO Scale

HO or H0 is the most popular scale of model railway in the world. According to the National Model Railroad Association (NMRA) standard S-1.2 predominantly used in North America, in HO scale, 3.5 mm (0.1378 in) represents 1 real foot (304.8 mm); this ratio works out to 1:87.0857142, usually rounded to 1:87.1.