By Zencalcy Editorial TeamLast reviewed About us
Mach number compares an object's speed with the local speed of sound. It is the natural scale for compressible flow: below 1 the flow is subsonic, near 1 transonic effects appear, and above 1 shock waves form. Because sound speed falls with temperature, the same ground speed gives a higher Mach number at altitude.
Convert between flow speed, sound speed and Mach number.
M = v / a
v is the flow or object speed and a is the local speed of sound. Mach number is dimensionless; the regime labels use the usual 0.8 and 1.2 boundaries.
| Symbol | Meaning |
|---|---|
| M | Mach number. |
| v | Speed relative to the medium. |
| a | Local speed of sound. |
With a = 343 m/s, M = 250 / 343 = 0.729. The same 250 m/s at 11 km altitude, where a is about 295 m/s, gives M = 0.847.
Continue with the Resonance Tube Calculator, Room Mode Calculator, or the Reverberation Time Calculator — or browse more acoustics and sound tools and all physics calculators.
No. It is 343 m/s in 20 °C air at sea level but about 295 m/s at the tropopause, because cold air carries sound more slowly. Aircraft Mach meters use outside air temperature.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Content updated: September 2026