The Railway Regulation (Gauge) Act 1846 or the Regulating the Gauge of Railways Act 1846 or the Gauge of Railways Act 1846 was an act of the Parliament of the United Kingdom, that was designed to standardise railway tracks. It was granted royal assent on 18 August 1846, and mandated that the track gauge – which was the distance between the two running rails' inner faces – of 4 feet 81⁄2 inches to be the standard for Great Britain and 5 feet 3 inches to be the standard for Ireland.