Speed of Sound Calculator
Clear airspeed calculations with consistent units.
ISA mode estimates temperature from altitude. Actual-temperature mode uses measured static air temperature; altitude is then unnecessary. Mach uses true airspeed, not groundspeed or indicated airspeed.
Formula & operating range
Speed of sound a = √(1.4 RT), with R = 287.05287 J/(kg·K) and T in kelvin. Mach = TAS / a. ISA temperature falls 6.5 °C/km to 11 km, then stays −56.5 °C to 20 km.
Dry, calorically perfect air model. ISA altitude range −1,000 to 20,000 metres; actual temperature −100 to 60 °C. TAS conversion is restricted to subsonic Mach, QNH 25–35 inHg and indicated altitude −2,000 to 60,000 ft. No humidity, instrument error or total-temperature correction is applied.
NASA: speed of sound and isentropic relations