The speed of sound is known as Mach 1. However, sound can travel through the atmosphere at varying speeds at different places and times, depending on the air pressure and air temperature.
Experiments and calculations in 1986 determined that at freezing temperatures, in dry air, sound travels about 741.1 miles an hour. At around 60 degrees Fahrenheit, sound travels faster, about 760 miles an hour.
When Chuck Yeager flew his Bell X-1 and broke the sound barrier, the speed of sound in his area was 662 miles per hour. His craft eventually reached Mach 1.06, or about 700 miles an hour.