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.
| 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 |