5 ft 3 in gauge railways

Currently, the suburban rail networks in Adelaide, Melbourne, and most regional lines in Victoria (including some that cross the border into New South Wales) use 5 ft 3 in (1,600 mm).

The 828 km (514.5 mi) long Melbourne–Adelaide rail corridor linking South Australia and Victoria, and some associated branch lines, was converted to standard gauge in 1995.

The final 200 km (124.3 mi) section of the North East line, Victoria and the 125 km (77.7 mi) long Oaklands railway line, which runs into New South Wales from Victoria, were converted to standard gauge in 2008–2010.

Following proposed projects of the Ulster Railway and Dublin and Drogheda Railway companies (using 6 ft 2 in (1,880 mm) and 5 ft 2 in (1,575 mm), respectively), and existing issues of competing gauges in Great Britain, in 1843 the Board of Trade (with the advice of engineers Charles Pasley and George Stephenson) introduced the gauge as a compromise.

Before the advent of diesel and electric traction, one of the advantages of the broader 5 ft 3 in (1,600 mm) Irish gauge compared to 4 ft 8+1⁄2 in (1,435 mm) was that more space between steam locomotive frames allows for a bigger firebox, enabling generation of more steam.