Kilometers Per Hour to Mach (km/h to Ma)

1 kilometer per hour equals 0.0008162876153 Mach (rounded).

1 kilometer per hour = 0.0008162876153 Mach

How to convert kilometers per hour to Mach

To convert kilometers per hour to Mach, multiply the number of kilometers per hour by 0.0008162876153. The factor is rounded to 10 significant digits. To go the other way, multiply Mach by 1,225.0584.

Mach = kilometers per hour × 0.0008162876153

Example: 10 kilometers per hour = 0.008162876153 Mach.

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

Kilometer Per Hour (km/h)

Metric (SI)Current unit

The standard unit for road speeds in most countries: 1 km/h is about 0.2778 m/s.

Myriameters per hour came first, at least in French. Although the meter was defined in 1799, speeds were initially quoted using the myriameter of 10,000 meters, and the phrase myriamètres par heure appears in 1802. The Dutch adopted the kilometer in 1817 under the name mijl. English abbreviations only appeared in the late nineteenth century, and many competing forms followed, from k. p. h. in 1889 to KMPH in 1940. Reuters and The Economist still prefer kph.

SI treats km/h as a unit symbol, not an abbreviation, and it is the generally preferred form. The European Union required SI usage in 1972, and a 1975 directive requires km/h on speedometers in all languages. In the United States a 1988 NHTSA rule allowed km/h on speedometers. Exactly 3.6 km/h make 1 m/s, one mile per hour is exactly 1.609344 km/h, and one knot is exactly 1.852 km/h. Road signs and speed limits in most of the world use it.

1 kilometer per hour = 0.2777777778 meters per second (approximately).

Sources: Wikipedia: Kilometres per hour; NIST Guide to the SI, Appendix B.8: conversion factors

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

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