The mile per hour is a unit of speed, expressing the number of international miles covered per hour.
It is currently the unit used for speed limits, and speeds, on roads in the United Kingdom, United States and other nations. It is also used to express the speed of delivery of a ball in various sporting events, such as cricket, tennis, and baseball at the higher levels of competition. A common abbreviation is mph or MPH, although mi/h is sometimes used in technical publications.
In the International System of Units (SI), the unit of speed or velocity is m/s. Road traffic speeds, in most countries, are quoted in km/h. Nautical and aeronautical applications, however, favour the knot as a common unit of speed: one knot is one nautical mile per hour.