Mach 3 is a speed measurement that is three times the speed of sound in a particular medium. The speed of sound varies depending on the medium it is traveling through, such as air, water, or a solid material. In dry air at sea level and at a temperature of 20 degrees Celsius (68 degrees Fahrenheit), the speed of sound is approximately 343 meters per second (1,235 kilometers per hour or 767 miles per hour). Therefore, if we multiply the speed of sound in air by 3, we get the speed of Mach 3, which is roughly 1,029 meters per second (3,704 kilometers per hour or 2,301 miles per hour).