Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 equals the speed of sound at that altitude and temperature. At sea level on a standard day (15°C), the speed of sound is approximately 661 knots (1,225 km/h).

Why does Mach number depend on altitude?

The speed of sound depends only on air temperature, which decreases with altitude in the troposphere (up to ~36,089 ft). Lower temperature means a lower speed of sound, so the same true airspeed corresponds to a higher Mach number at higher altitudes.

What is the difference between subsonic, transonic, and supersonic?

Subsonic flight is below Mach 0.8, transonic is roughly Mach 0.8–1.2 (where shock waves begin forming), and supersonic is above Mach 1.2. Hypersonic flight typically refers to speeds above Mach 5.

Does this calculate indicated or true airspeed?

The speed input is treated as true airspeed (TAS). Mach number is computed as TAS divided by the local speed of sound. If you have indicated airspeed, use the True Airspeed Calculator first to convert it.

What temperature model does this use?

The ISA (International Standard Atmosphere) model: sea-level temperature 15°C, lapse rate of 1.9812°C per 1,000 ft up to the tropopause at 36,089 ft, then constant -56.5°C in the stratosphere. You can override OAT for non-standard conditions.

Mmo (Maximum Operating Mach number) is a speed limit found on many jet aircraft. It is typically around Mach 0.82–0.92 for commercial airliners and prevents transonic shock-induced control problems. This calculator can convert Mmo to an equivalent true airspeed for your planning altitude.

Mach Number Calculator

Name: Mach Number Calculator
Availability: InStock
Author: Nham Vu

Enter your speed and altitude to calculate Mach number, or convert Mach number back to knots, km/h, and mph.