N gauge

N scale
Model of an N scale 2-6-6-2 Mallet locomotive, shown alongside a pencil for size
Scale ratio	1:160
Model gauge	9 mm (0.354 in)
Prototype gauge	Standard gauge

N scale is a popular model railway scale. Depending upon the manufacturer (or country), the scale ranges from 1:148 to 1:160. In all cases, the gauge (the distance between the rails) is 9 mm or 0.354 in. The term N gauge refers to the track dimensions, but in the UK in particular N gauge refers to a 1:148 scale with 1:160 (9 mm or 0.354 in) track gauge modelling. The terms N scale and N gauge are often inaccurately used interchangeably, as scale is defined as ratio or proportion of the model, and gauge only as a distance between rails. The scale 1:148 defines the rail to rail gauge equal to 9 mm or 0.354 in exactly (at the cost of scale exactness), so when calculating the rail and/or track use 1:148 and for engines and car wheel base use 1:160.

All rails are spaced 9 mm apart but the height can differ. Rail height (in thousandths of an inch) is expressed as a "code": thus, Code 55 rails are 0.055 ins high while Code 80 rails have a height of 0.080 ins. Real railroad rails are at least 6 ins tall and can be taller on some roads, so at true scale the rails would be about 0.040 ins high. Many older N scale models may not run well on Code 55 track as their flanges are often unrealistically large, causing the wheels to bounce along the ties instead of ride along the railhead. Wheelsets with these large flanges are colloquially known as 'pizza cutters' due to a resemblance to the kitchen utensil.

An advantage of N scale is that it allows hobbyists to build layouts that take up less space than HO scale, or put longer track runs into the same amount of space, because the models are smaller (by nearly a half) than they are in HO scale (1:87). While N scale is quite small, it is not the smallest commercially available scale, as Z scale is smaller yet at 1:220 and T scale is 1:450 or 1:480. N scale is considered generally compatible with 1:144 scale for miniature wargaming.

Although trains and accessories of similar gauge and/or scale existed as early as 1927, modern commercially produced N scale models were first launched by the Arnold company of Nuremberg in 1962. Unlike other scales and gauges, which were de facto standards at best, within two years N scale manufacturers defined the gauge and voltage, as well as the height and type of couplers. For example, Arnold developed the now ubiquitous "Rapido" coupler to provide a simple and robust releasable coupler design. Although the original Arnold coupler has been joined by more functional and aesthetically pleasing designs, Arnold allowed use of the Rapido design by other manufacturers, so established a common standard to couple together rolling stock from different sources.