Metrication
![A speedometer used in American and British cars, showing the speed of the vehicle in miles per hour (outer, in white) and kilometres per hour (inner, in red) – for Canadian[1] vehicles the scales are reversed](/Images/godic/202501/27/Speedometer-dualsystem5156.jpeg")
![A speedometer from an Australian car, showing the speed of the vehicle only in km/h, as in almost all countries.](/Images/godic/202501/27/Camry_Speed_Odometer5156.jpg")
![An example of metrication in 1860 when Tuscany became part of modern Italy](/Images/godic/202501/27/Tabella_conversione_metrica_1860_MG_77715156.jpg")
![Countries by date of metrication. Colours red to green show the pattern of metrication from 1795 to 1998. Black identifies countries that have not adopted the metric system as the primary measurement system. White identifies countries that already used the metric system at the time they gained their independence.](/Images/godic/202501/27/Metrication_by_year_map.svg5156.png")
Metrication or metrification is conversion to the metric system of units of measurement. Worldwide, there has been a long process of independent conversions of countries from various local and traditional systems, beginning in France during the 1790s and spreading widely over the following two centuries, but the metric system has not been fully adopted in all countries and sectors.