Mach to Knots (Ma to kn)

1 Mach equals 661.4786177 knots (rounded).

How to convert Mach to knots

To convert Mach to knots, multiply the number of Mach by 661.4786177. The factor is rounded to 10 significant digits. To go the other way, multiply knots by 0.001511764664 (rounded).

knots = Mach × 661.4786177

Example: 10 Mach = 6,614.786177 knots.

Approximate value. Standards for the Mach varied by place and period, so this converter uses the most commonly cited value. Treat results as estimates, not exact figures.

About these units

Mach (Ma)

ScientificCurrent unitApproximate value

The speed of sound at sea level in standard conditions (15 °C): about 340.294 m/s or 1,225 km/h. The speed of sound varies with temperature and altitude.

Ernst Mach, the Austrian physicist and philosopher born in Moravia in 1838, never defined a unit of speed, yet the ratio carries his name. In 1887 he and Peter Salcher presented a paper on photographing processes in air caused by projectiles, including a shadowgraph of the bow shock around a supersonic bullet fired from a Werndl carbine. The ratio of flow speed to the local speed of sound was later named for him.

Mach is therefore a dimensionless number, not a fixed speed, and because the speed of sound depends on temperature, so does Mach 1. It is about 340 m/s (1,225 km/h) in dry air at 15 °C at sea level, 343 m/s at 20 °C, and about 295 m/s above 11 kilometers where the air is cold. Flight is called subsonic below 0.8, transonic from 0.8 to 1.2, supersonic from 1.2 to 5 and hypersonic from 5 to 10. On 14 October 1947 Chuck Yeager flew the Bell X-1 to Mach 1.06, reported as 361 m/s.

1 Mach = 340.294 meters per second (approximately).

Sources: Wikipedia: Mach number; Wikipedia: Ernst Mach; Wikipedia: Speed of sound

Knot (kn)

NauticalCurrent unit

One nautical mile per hour, exactly 1.852 km/h. The unit of speed for ships, aircraft and wind.

Knots in a rope really were counted. Before the mid-nineteenth century, sailors threw a weighted wooden board, the chip, off the stern on a line called the log-line. The line carried knots at regular intervals, and a sailor counted how many passed through his fingers while another timed the run with a sandglass. William Bourne's A Regiment for the Sea, printed in 1574, is the first known description, and many ships spaced knots 8 fathoms, about 14.6 meters, apart with a glass of roughly half a minute.

Today a knot is one nautical mile per hour, exactly 1,852 meters per hour, about 1.151 mph or 0.514 m/s. A ship making 1 knot along a meridian covers about one minute of latitude per hour, which is why charts and the unit fit together. It is not an SI unit, and the symbol is kn, though kt is common in aviation. Saying knots per hour is wrong, since that would describe acceleration. The US moved civil aircraft standards to nautical miles and knots in 1969, and winds and currents are also quoted in them.

1 knot = 0.5144444444 meters per second (approximately).

Sources: Wikipedia: Knot (unit); Wikipedia: Chip log; NIST Guide to the SI, Appendix B.8: conversion factors

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