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 . The term N "gauge" refers to the track dimensions, but in the United Kingdom in particular British N gauge refers to a 1∶148 scale with 1∶160 () 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 exactly (at the cost of scale exactness), so when calculating the rail or track use 1∶160 and for engines and car wheel base use 1∶148.