The kilometer, which is internationally spelled as kilometre, as prescribed by the organisation, International Bureau of Weights and Measures, has 'km' as its SI symbol and is the preferred unit of distance. Kilometer had been created as the unit of length for use in the prevalent metric system. It is equal to exactly one thousand metres, as is evident from the letter 'kilo' which is the SI prefix for 1000. It is internationally recognized as the unit of measurement used officially for the purpose of expressing distances between different geographical location, in most countries around the world. The primary exceptions to its use include the United States and also the road network in the UK, where 'mile' is the officially used unit.
As the history of the kilometer goes, by the 8th of May, 1790 decree, the French Constituent assembly passed an order for the renowned 'French Academy of Sciences', asking it to develop a brand new system of measurement. Later, in the month of August of the year 1793, the respected, French National Convention passed a decree making the unit 'metre' as the only length measurement system to be used witin the French Republic. The kilometer was first named "Millaire". Even though, the unit 'metre' was actually formally defined only in 1799, the "myriametre" or 10,000 metres was the preferred term rather than "kilometre" for regular, everyday use. This term, "myriamètre" is observed to have appeared several times in the texts of Develey's book, titled Physique d'Emilewhich was published in the year 1802. In this book, the term 'kilometre' only appears in the appendix. Also, French maps which were published in the year 1835 are seen to have scales that show myriametres and postal leagues or "lieues de Poste" equal to about 4,288 metres.
In a similar cultural convention, the Dutch people adopted the use of 'kilometre' in the year 1817 but named it the 'mijl'. It was much later, in the year 1867 that "kilometer" became the sole official unit used for measurement in the Netherlands and it represented 1000 metres. Also, two different German textbooks from the year 1842 and 1848 give a clear picture about the use of 'kilometre' across the European nations. While one shows that the kilometre was used throughout the Netherlands and also in Italy, the other shows that the myriametre was used in France.
In the year 1935, the widely respected, 'International Committee for Weights and Measures', abolished use of the prefix "myria" and along with it, the use of "myriametre". This left the term kilometre as the only recognised standard unit of length for all measurements near its magnitude.
The current usage varies in the United Kingdom, with road signs showing distances in miles, while at the same time, location-marker posts which are used for the purpose of reference by road construction engineers and also most emergency services personnel show the distance references in an unspecified unit which are kilometer based. Thus it's usage varies in different fields and departments.
In the US, however, the stated National Highway System Designation Act, 1995 bans the federal highway funds from being used for the purpose of converting existing signs to metric units or purchasing new signs which have metric units on display. The Executive Director of the government's US Federal Highway Administration, Mr Jeffrey Paniati, had once written in a memo in 2008 that the Section 205 (c) (2) of National Highway System Designation Act passed in 1995 disallows the US from needing any State Department of Transport to officially use the metric system for any project development activity. Thus the unit is widely used today for measurement of distance.
Conversion from kilometers to miles is simple if one remembers the constant that is to be used in the calculation. One can easily master the formula to be used for converting measurements from kilometers to miles. One kilometer is exactly equal to 0.621371 miles and you can simply keep in mind the number 0.62, which is widely used for this purpose. In reverse, one mile is exactly equal to 1.609344 kilometers. Therefore, in order to convert values from kilometers to miles, one can simply multiply the values in kilometers by 0.62137.
Here is a sample calculation, to help you better understand the conversion process. Suppose one starts with five kilometers. Some people maybe interested in the conversion of this value as they may want to know the number miles in a '5K' run. The formula to be used here is 5 X 0.62, which gives 3.1 miles. The opposite conversion can be carried out similarly. In this manner, one can convert kilometers to miles and vice versa.