The standard railway gauge is

The standard railway gauge is 143cm. The railway gauge is the distance between the inner sides of the two parallel rails that make up a railway track. The standard gauge of 143cm was adopted as an international standard because it provides a good balance between stability and flexibility for trains. A wider gauge provides greater stability but makes the track more expensive to build, while a narrower gauge is cheaper but less stable, which can cause derailments. The 143cm gauge is used in many countries around the world, including the United States, Canada, Australia, and most of Europe, among others.