Mach Number Calculator
Compares a speed with the local speed of sound.
Mach number
— Ma
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Speed of sound used —
Regime —
The formula
Ma = v ÷ a a = √(γ R T ÷ M)
For dry air, γ = 1.4 and M = 28.96 g/mol. In an ideal gas, the speed of sound depends on temperature and not on pressure. Use true airspeed, not indicated airspeed.
What to watch out for
The same speed is a higher Mach number at altitude, as the air is colder there.
Frequently Asked Questions
What Mach number is 900 km/h at −50 °C?
About 0.83.
How fast is Mach 1?
About 1,225 km/h at 15 °C, and 1,078 km/h at −50 °C.