Several years ago (1995) an explanation of how Standard Track Gauge measurements were handed down from ancient times was widely circulated around the Internet. While this description is a joy to behold, it can't be verified by independent analysis. Both the fanciful explanation and a more reasoned approach are presented here for your edification and further enlightenment.
A More Reasoned Analysis
The only standard gauge in the U.S. is a defacto 4' 8 1/2" as recommended by the A.R.A. committee on standard wheel and track gauges in October of 1896. Great Britain, on the other hand, has a true standard track gauge of the same dimensions because it was mandated by an act of Parliament in 1846 that all railroads should be built to the same gauge as the Stockton and Darlington, England's (and the world's) first public rail line to use locomotives.
America had a multiplicity of gauges at the beginning of the Civil War, but the modern standard was most common in New England and 5' was the standard in the South. During the course of the war, as a railroad was captured by one side or the other it would often be torn up by the retreating side and then rebuilt at the desired gauge by the victors. Some lines changed hands and gauges more than once during the war. After the war, economic pressures were put on the southern lines to change, but it wasn't until 1886 that representatives of the lines agreed to the change. All of the lines were re-gauged on May 31st and June 1st of that year in a massive effort. Huge crowds turned out all through the south to watch the event.
Most of Canada made a voluntary changeover in 1880, followed by Mexico. When the Louisville and Nashville line finally changed gauge in 1901, almost the last in the U.S. to do so, roughly 82% of North American lines were "Standardized".
|Broad gauge (India/BART):||1676 mm||5' 6"||Broad gauge (Spain):||1674 mm||5' 5 9/10th"|
|Broad gauge (Portugal):||1665 mm||5' 5 11/20th"|
|Broad gauge (Ireland):||1600 mm||5' 3"|
|Broad gauge (Finland):||1524 mm||5' exactly|
|Broad gauge (former USSR):||1520 mm||5'|
|Standard gauge:||1435 mm||4' 8 1/2"|
|Narrow gauge (Cape gauge):||1067 mm||3' 6"|
|Narrow gauge (meter gauge):||1000 mm||3' 3 37/100"|
|Narrow gauge (US narrow):||914 mm||3' 0"|