Convert a speed in km/h to its Mach number at typical jet cruise altitude.
Convert a speed into its Mach number — how many times faster than the local speed of sound it is — with an honest choice of reference condition, since Mach number genuinely depends on which one you use.
This is the detail most speed-to-Mach converters skip: the speed of sound isn't a fixed constant, it depends on air temperature, and temperature varies a lot with altitude. At sea level (15°C), sound travels at about 340 m/s. At typical jet cruise altitude (around 36,000 feet, in the stratosphere at roughly −56.5°C), it's slower, around 295 m/s, because colder air carries sound more slowly. The same physical speed is a higher Mach number at altitude than it would be at sea level — which is exactly why Concorde's well-known "Mach 2" cruise speed (about 2,180 km/h) only actually computes to Mach 2 using the cruise-altitude reference; using a sea-level reference for the same speed gives a noticeably different, lower number.
Pick whichever reference matches what you're actually asking about — sea level for something like a car, wind speed, or a sea-level weapon system; cruise altitude for a commercial or supersonic aircraft, which is where the "Mach 1," "Mach 2" figures you've likely heard quoted actually come from.
Mach number is a ratio to the local speed of sound, and the speed of sound depends on air temperature — colder air (like the stratosphere at cruise altitude) carries sound more slowly than air at sea level. The same physical speed is a higher Mach number where sound travels slower.
It does, once you select the cruise-altitude reference — Concorde’s well-known ~2,180 km/h cruise speed computes to almost exactly Mach 2.04 at cruise altitude, matching the documented figure. At a sea-level reference, the same speed computes to a noticeably lower Mach number, since sea-level air carries sound faster.
Yes, continuously — this tool uses two common reference points (sea level and standard cruise altitude) rather than modeling every altitude, since those two cover the overwhelming majority of real questions people ask this kind of tool.