The mile per hour's a unit of speed, expressing the number of international miles covered per hour. It's currently the unit used for speed limits, and speeds, on roads in the United Kingdom and United States. It's 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's mph or MPH. In the International System of Units (SI), the unit of speed or velocity's m/s. Road traffic… (More on Mph)