7 mm scale, also known as British O scale, is a model railway scale of 1:43.5 (or 7 mm to 1 ft; hence its name). The scale is thus different from American O scale (1:48) and European O scale (1:45). For standard gauge railways, 32mm gauge, or 0 gauge is most commonly used. ScaleSeven (S7) standard however specifies 33 mm gauge, which is closer to scale. For narrow gauge modelling, 16.5 mm gauge
Name Model gauge Scaled gauge Prototype gauge Prototype standard gauges British 0 gauge 32 mm (0 gauge) 4' 6¾" Standard gauge ScaleSeven (standard) 33 mm 4' 8½" Prototype broad gauges ScaleSeven (Irish) 36.75 mm 5' 3" ScaleSeven (Great Western) 49.2 mm 7' 0¼" Great Western broad gauge Prototype narrow gauges O21 21 mm 3' O16.5 16.5 mm (H0 gauge) 2' 4¼" 2' - 2'6" O14 14 mm 2' O9 9 mm (N gauge) 15½"
References