Railways with a track gauge of 3 ft 6 in were first constructed as horse-drawn wagonways. The first intercity passenger railway to use 3 ft 6 in was constructed in Norway by Carl Abraham Pihl. From the mid-nineteenth century, the 3 ft 6 in gauge became widespread in the British Empire. In Africa it became known as the Cape gauge as it was adopted as the standard gauge for the Cape Government Railways in 1873, although it had already been established in Australia and New Zealand before that. It was adopted as a standard in New Zealand, South Africa, Indonesia, Japan, the Philippines, Taiwan, and Queensland in Australia.

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.