Railways with a railway track gauge of 5 ft first appeared in the United Kingdom and the United States. This gauge became commonly known as "Russian gauge", because the government of the Russian Empire chose it in 1843. Former areas and states of the Empire have inherited this standard. However in 1970, Soviet Railways re-defined the gauge as 1,520 mm.

In rail transport, track gauge is the distance between the two rails of a railway track. All vehicles on a rail network must have wheelsets that are compatible with the track gauge. Since many different track gauges exist worldwide, gauge differences often present a barrier to wider operation on railway networks.