Mach 1 (the speed of sound in air) equals about
1.234,8 km/h
The Mach number is not a fixed unit, but a ratio between an object's speed and the speed of sound in the medium it's moving through. At sea level and standard temperature (15°C), the speed of sound in air is about 343 meters per second, or 1,234.8 km/h: this value corresponds to Mach 1. The speed of sound varies with temperature and altitude, so Mach 1 is not exactly the same km/h value at every altitude.
To convert from Mach to km/h (at sea level), multiply the Mach number by 1,234.8:
To convert from km/h to Mach, perform the inverse operation, dividing by 1,234.8:
The Mach number is used in aeronautics and aerospace to describe speeds close to, equal to, or exceeding the speed of sound, where an aircraft's aerodynamic properties change significantly (crossing the 'sound barrier'). It is also a term of general knowledge, often associated with supersonic military aircraft or spacecraft.