SPEED OF SOUND AT DIFFERENT ALTITUDES


Mach 1.0 is the speed of sound in air, so a plane flying Mach 2.0 is flying twice as fast as the speed of sound. The speed of sound is not a constant, but depends on altitude (or actually the temperature at that altitude). A plane flying Mach 1.0 at sea level is flying about 1225 km/h (661 Knots, 761 mph), a plane flying Mach 1.0 at 30000 ft is flying 1091 km/h (589 knots, 678 mph) etc. Speeds below Mach 1 are called subsonic, between Mach 0.8-1.2 Transonic and above Mach 1.2 Supersonic.

ALTITUDE
TEMPERATURE
SPEED OF SOUND
Feet (ft) Meter (m) Celcius (°C) Kelvin (K) mph knots km/h m/s
0 (sea level) 0 (sea level) 15 288 761.1 661 1,225 340.3
5,000 1524 5.1 278 747.9 650 1,204 334.4
10,000 3048 -4.8 268 734.5 638 1,182 328.4
15,000 4572 -14.7 258 720.8 626 1,160 322.2
20,000 6096 -24.6 248 706.9 614 1,138 316.0
25,000 7620 -34.5 239 692.6 602 1,115 309.6
30,000 9144 -44.4 229 678.1 589 1,091 303.1
35,000 10668 -56.0 217 660.7 574 1,063 295.4
40,000 12192 -56.6 216 659.8 573 1,062 294.9
45,000 13716 -56.6 216 659.8 573 1,062 294.9
50,000 15240 -56.6 216 659.8 573 1,062 294.9
55,000 16764 -56.6 216 659.8 573 1,062 294.9
60,000 18288 -56.6 216 659.8 573 1,062 294.9




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