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Aviation glossary

Mach number

Also: Mach, Mach speed

Weights and performance

Ratio of an aircraft's speed through the air to the speed of sound in that air; Mach 1 means flying at exactly the speed of sound.

What it is

It is named after the Austrian physicist Ernst Mach. The speed of sound is not fixed: it depends on air temperature. At sea level, at 15 °C, it is about 1,225 km/h; at 11,000 metres, where the air is around −56 °C, it drops to about 1,060 km/h. The same Mach number therefore corresponds to different speeds at different altitudes.

At high altitude, what limits a jet is not so much its speed in km/h as its Mach number: as it approaches Mach 1, shock waves form over the wing and drag rises sharply. That is why airliners cruise between Mach 0.78 and 0.85, and above a certain altitude pilots fly by reference to Mach rather than indicated airspeed.

Below about Mach 0.8 flight is described as subsonic, between roughly 0.8 and 1.2 as transonic, and above that as supersonic. Concorde cruised at around Mach 2.

On Vuelopedia

The technical data on a Vuelopedia model page gives the cruise speed in km/h and as a Mach number.

Related terms

Cruise speedSpeed at which an aircraft flies most of a journey, in level flight at high altitude, chosen to balance fuel burn, time and cost. KnotUnit of speed used in aviation and at sea, equal to one nautical mile per hour, which is exactly 1.852 km/h. Swept wingWing whose edges angle backwards from the fuselage to delay compressibility effects, allowing an aircraft to cruise closer to the speed of sound. Service ceilingHighest altitude at which an aircraft can operate normally, set either by its ability to keep climbing or by the limit fixed in its certification. CruiseThe central and usually longest phase of a flight, in which the aircraft flies level at its most efficient height and speed between the climb and the descent.
Whole glossary

Cite

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This page was last updated on October 9, 2026

APA

Vuelopedia. (2026, October 9). Mach number. Retrieved October 16, 2026, from https://vuelopedia.org/en/glossary/mach-number

MLA

“Mach number.” Vuelopedia, Fundación Poderia, 9 Oct. 2026, vuelopedia.org/en/glossary/mach-number. Accessed 16 Oct. 2026.

Chicago

Vuelopedia. “Mach number.” Fundación Poderia. Last modified October 9, 2026. https://vuelopedia.org/en/glossary/mach-number.

Harvard

Vuelopedia (2026) Mach number. Available at: https://vuelopedia.org/en/glossary/mach-number (Accessed: 16 October 2026).

BibTeX

@misc{vuelopedia_en_glossary_mach_number,
  author       = {{Vuelopedia}},
  title        = {{Mach number}},
  publisher    = {Fundación Poderia},
  year         = {2026},
  date         = {2026-10-09},
  url          = {https://vuelopedia.org/en/glossary/mach-number},
  howpublished = {\url{https://vuelopedia.org/en/glossary/mach-number}},
  urldate      = {2026-10-16},
  note         = {Accessed 2026-10-16}
}

Wikipedia

{{cite web |url=https://vuelopedia.org/en/glossary/mach-number |title=Mach number |website=Vuelopedia |publisher=Fundación Poderia |date=2026-10-09 |access-date=2026-10-16 |language=en}}

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