N scale is a popular model railway scale. Depending upon the manufacturer (or country), the scale ranges from 1:148 to 1:160. Effectively the scale is 1:159, 9 mm to 1,435 mm (4 ft 8+1⁄2 in), which is the width of standard gauge railway. However the scale may vary to simulate wide or narrow gauge rail. 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 United Kingdom in particular British 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 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.