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Miles per hour (abbreviated mph, MPH or mi/h) is an imperial and United States customary unit of speed expressing the number of statute miles covered in one hour. Although kilometres per hour is now the most widely used measure of speed, miles per hour remains the standard unit for speed limits in the United States, the United Kingdom, Antigua & Barbuda and Puerto Rico, although the latter two use kilometres for long distances.
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Usage
Road traffic speeds in some countries and territories are indicated in miles per hour, as follows:
Miles per hour is the unit also used in the Canadian rail system, which uses km/h on roads. In some countries mph may be used to express the speed of delivery of a ball in sporting events such as cricket, tennis and baseball.
Road traffic speeds in other countries are indicated in kilometres per hour, while occasionally both systems are used. For example, in Ireland, a judge considered a speeding case by examining speeds in both kilometres per hour and miles per hour. The judge was quoted as saying the speed seemed "very excessive" at 180 km/h but did not look "as bad" at 112 mph; a reduced fine was still imposed on the speeding driver.
Nautical and aeronautical usage
Nautical and aeronautical applications, however, favour the knot as a common unit of speed. (One knot is one nautical mile per hour, with a nautical mile being exactly 1,852 meters or about 6,076 feet.)
(Values in bold face are exact.)
1 Mph = 0.000277778 Mps (Miles Per Second)
Example: Apollo 11 attained speeds of 25,000 Mph, which converts to about 7 Mps. If Apollo 11 were to travel at 25,000 Mph from New York to Los Angeles it would reach Los Angeles in under 6 minutes.