Miles per hour (mph) is the standard speed unit in the United States, United Kingdom, and a few other countries, used for speed limits, vehicle speedometers, and weather forecasts. American road signs exclusively display speed limits in mph, and car enthusiasts commonly reference 0-60 mph times as a performance benchmark. One mile per hour equals exactly 1.60934 kilometers per hour.

Mach (Ma) is a dimensionless speed unit representing the ratio of an object's speed to the speed of sound in the surrounding medium. At sea level under standard conditions, Mach 1 equals approximately 343 meters per second or 1,235 kilometers per hour, though this varies with altitude and temperature. Supersonic aircraft travel above Mach 1, while hypersonic vehicles exceed Mach 5.