Speed Converter
Convert speed between mph, km/h, m/s, knots, and Mach instantly. Free online speed unit converter.
Mach value at sea level, 20°C (≈ 340.3 m/s)
Frequently Asked Questions
What is Mach number?
Mach number is the ratio of an object's speed to the speed of sound in the surrounding medium. Mach 1 equals the speed of sound, which is approximately 340.3 m/s (1,225 km/h) at sea level and 20°C. Objects moving faster than Mach 1 are said to be supersonic. The Mach number varies with altitude and temperature.
What is the difference between knots and km/h?
A knot is one nautical mile per hour, where a nautical mile is 1,852 metres — approximately 1.852 km. Therefore, 1 knot ≈ 1.852 km/h. Knots are the standard unit of speed in aviation and maritime navigation because they relate directly to latitude degrees on a nautical chart, simplifying navigation calculations.
What is the speed of sound?
The speed of sound is approximately 343 m/s (1,235 km/h or 767 mph) at 20°C at sea level in dry air. It changes with temperature, pressure, and the medium through which it travels. In water, sound travels about 4.3 times faster than in air. At higher altitudes where temperature drops, the speed of sound decreases.