2 ft 6 in gauge railways are narrow gauge railways with track gauge of 2 ft 6 in. This type of rail was promoted especially in the colonies of the British Empire during the second half of the nineteenth century by Thomas Hall and Everard Calthrop.

Everard Richard Calthrop was a British railway engineer and inventor. Calthrop was a notable promoter and builder of narrow-gauge railways, especially of 2 ft 6 in narrow gauge, and was especially prominent in India. His most notable achievement was the Barsi Light Railway, but he is best known in his home country for the Leek and Manifold Valley Light Railway. Calthrop has been described as a "railway genius". Later in life he took an interest in aviation, patenting some early designs for parachutes.