Mach Number Calculator
Mach number from speed and air temperature (or altitude), the local speed of sound, and the flight regime — subsonic to hypersonic.
How it works
M = v ÷ a, a = √(γ R T) = √(1.4 × 287.05 × T_kelvin)
Mach number compares speed with the local speed of sound, which depends only on temperature — about 340 m/s at sea level but 295 m/s at cruising altitude, where the air is −56 °C. That is why an airliner at 900 km/h is Mach 0.85 up high but would be only Mach 0.73 at the surface. Shock waves form as M approaches 1; above Mach 5 heating dominates design.
Worked example
900 km/h (250 m/s) at 11,000 m (−56.5 °C): a = 295 m/s → Mach 0.85.
Frequently asked questions
Does humidity matter?
Slightly — humid air is less dense and sound travels about 0.5% faster in saturated air.
What is the speed of sound in water?
About 1,480 m/s — Mach numbers for submarines are computed against that, though rarely used.
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This calculator is for educational purposes. Double-check important results before acting on them.