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.