How fast is mach nine?
Mach 9 would be about 5900 mph, at a reasonable altitude of 80000 feet. The Mach number is based on the speed of sound, which gets slower the higher your altitude. At sea level, Mach 9 would be closer to 6750 mph, but it would be very unusual for an aircraft to fly so fast that low.
The speed of Mach 9 (where Mach 1 is speed of sound) equals to 11113 km per hour (6905 mi per hour).
Mach 9 is equal to 6,669.8729 Miles per Hour or 10,734.12 Kilometers per Hour.
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