Speed Unit Conversion Guide
Speed is expressed in different units depending on context: km/h for road traffic in most countries, mph in the US and UK, m/s in scientific contexts, knots for maritime and aviation, and Mach for supersonic flight. Each unit has a fixed conversion to m/s (the SI unit), making all conversions straightforward via the base unit.
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Formula
Speed Converter
Convert speed between km/h, mph, m/s, knots, and Mach number.
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Worked Example
Given:
Related Calculators
FAQs
What is a knot?
A knot is one nautical mile per hour (1.852 km/h). It is used in maritime and aviation navigation because nautical miles relate to geographic coordinates (one nautical mile = one arcminute of latitude). A ship travelling at 20 knots covers 20 nautical miles per hour.
What is Mach number?
Mach number is the ratio of an object's speed to the speed of sound in the surrounding medium. The speed of sound in air at sea level and 20°C is approximately 343 m/s. Mach 1 = speed of sound. Mach 2 = twice the speed of sound. The speed of sound varies with temperature, altitude, and medium.
Why do the US and UK still use mph for road speed?
Both countries retained mph when most of the world adopted km/h. The UK officially uses km/h for scientific purposes but mph for road traffic. Changing road signs and vehicle speedometers nationwide would be enormously costly. Most UK cars show both mph and km/h on the speedometer.