Speed of Sound Calculator

How it works

a = 38.97 × √(OAT in kelvin), in knots. Pressure and density cancel out of the physics — only temperature is left, which is why the speed of sound falls as you climb: at ISA sea level (15 °C) it is about 661 kt, and at the −56.5 °C of the tropopause about 573 kt.

Why it matters below Mach 1

Long before any airframe limit, the local speed of sound sets the Mach number your true airspeed represents — and Mach effects (buffet, tuck, critical Mach) arrive at a fixed Mach, not a fixed airspeed. Cold air means a lower speed of sound, which means the same TAS is a higher Mach. See the Mach calculator.