Speed Converter

100 km/h equals 62.14 mph. The conversion factor is 1 km/h = 0.621371 mph, derived from the exact definition that 1 mile = 1.609344 km. A quick mental shortcut: multiply km/h by 0.62 for a close estimate.

A knot is exactly 1 nautical mile per hour, which works out to 1.852 km/h or about 1.1508 mph. Nautical miles are based on the Earth's circumference, which is why knots are the standard speed unit in both maritime navigation and aviation worldwide.

Mach 1 is the speed of sound. This converter uses the standard sea-level value at 15 degrees C (59 degrees F), which is 340.29 m/s, or about 1,225 km/h (761 mph). At higher altitudes where air is colder and thinner, the speed of sound drops, so Mach 1 at cruising altitude is closer to 295 m/s.

Miles per hour appears on road signs in the US, UK, and a small number of other countries. Kilometers per hour is the standard everywhere else, including the EU, Canada, and Australia. Aviation and shipping use knots globally, regardless of the local land-speed convention.

Multiply by 3.6. That factor comes directly from the unit definitions: 1 m/s x 3,600 s/hr / 1,000 m/km = 3.6 km/h. So 10 m/s is exactly 36 km/h, which is roughly the top speed of a road cyclist at full effort.