(*) The speed at which sound travels in a given medium under specified conditions. The speed of sound at sea level in the International Standard Atmosphere is 1108 ft/second, 658 knots, 1215 km/hour. See also hypersonic; sonic; subsonic; supersonic; transonic.
The speed of sound is the distance traveled per unit time by a sound wave propagating through an elastic medium. The SI unit of speed is the metre per second (m/s). In dry air at , the speed of sound is . This is , or a kilometre in or a mile in .