Mach Number Calculator
Calculate Mach number from airspeed and altitude.
Convert between TAS, EAS, CAS, and Mach number.
Find the speed of sound at any altitude and temperature.
Speed of Sound in Air The speed of sound depends on temperature, not pressure: a = √(γ × R × T) = 20.05 × √T (m/s) where T is in Kelvin At sea level (15°C = 288.15 K): a = 340.3 m/s = 661.5 knots = 1225.4 km/h = 761.2 mph For every °C temperature drop, sound speed decreases by ~0.6 m/s.
ISA Standard Atmosphere International Standard Atmosphere (ISA) defines temperature vs altitude: Sea level: 15°C (288.15 K), pressure 1013.25 hPa Lapse rate: −6.5°C per 1000 m up to 11,000 m (tropopause) Tropopause (11,000–20,000 m): constant −56.5°C (216.65 K) Above 20,000 m: temperature increases again
Mach Number M = V / a Where V = true airspeed (TAS), a = local speed of sound. Subsonic: M < 1 | Transonic: 0.8 < M < 1.2 | Supersonic: 1 < M < 5 | Hypersonic: M > 5
Mach Regimes M < 0.3: incompressible flow — simple Bernoulli applies M 0.3–0.8: compressible subsonic — correction factors needed M 0.8–1.2: transonic — shock waves begin forming M > 1: supersonic — oblique shock waves, sonic boom M > 5: hypersonic — extreme heating, plasma effects
Critical Mach Number (Mcrit) For aircraft with subsonic design, airflow over the wing can reach M=1 locally. This causes control problems and buffeting — the “coffin corner.” Airliners typically cruise at M 0.78–0.86 to stay below Mcrit. Concorde cruised at M 2.04; SR-71 Blackbird at M 3.2.