7 mm scale

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).^[1] The scale is thus different from American O scale (1:48)^[1] and European O scale (1:45). For standard gauge railways, 32mm gauge, or 0 gauge is most commonly used.^[1] ScaleSeven (S7) standard however specifies 33 mm gauge, which is closer to scale.^[1] 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"[citation needed]	Standard gauge
ScaleSeven (standard)	33 mm	4' 8½"	4 ft 8+1⁄2 in (1,435 mm) standard gauge
Prototype broad gauges
ScaleSeven (Irish)	36.75 mm	5' 3"	5 ft 3 in (1,600 mm) Irish gauge
ScaleSeven (Great Western)	49.2 mm	7' 0¼"	7 ft (2,134 mm) Great Western broad gauge
Prototype narrow gauges
O21	21 mm	3'	3 ft (914 mm)
O16.5	16.5 mm (H0 gauge)	2' 4¼"	2' - 2'6"
O14	14 mm	2'	2 ft (610 mm)
O9	9 mm (N gauge)	15½"	15 in (381 mm)

7 mm scale
O gauge layout at the Trains and Boats exhibition
Scale	7 mm to 1 ft
Scale ratio	1:43.5
Model gauge	multiple