Miles per Hour to Kilometers per Hour Converter

Speed is distance divided by time, and its SI unit is the metre per second (m/s). The two most common everyday units are the kilometre per hour (km/h) and the mile per hour (mph): one metre per second is exactly 3.6 km/h and about 2.237 mph, while 1 km/h is about 0.621 mph. At sea and in the air, speed is measured in knots — one knot is one nautical mile per hour, or exactly 1.852 km/h. Very high speeds use the Mach number, the ratio of an object's speed to the local speed of sound; at sea level in standard conditions that is about 340.29 m/s (1,225 km/h), but it falls as air gets colder or thinner, so Mach 1 is not a fixed speed. The ultimate limit is the speed of light in a vacuum, exactly 299,792,458 m/s. Every unit here is stored as its exact number of metres per second, so any conversion is just the input turned into m/s and then into the target unit. Note that running or cycling pace (minutes per kilometre or per mile) is the reciprocal of speed rather than a linear unit, so it is handled by a separate pace calculator and is not part of this tool.