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.
(S7) standard however specifies 33 mm gauge, which is closer to scale.
For narrow gauge modelling, 16.5 mm gauge
References
{{Model-rail-stub