Original: In dry air at 20 °C (68 °F), the threshold value required for an object to be traveling at a supersonic speed is approximately 343 m/s, (1,125 ft/s, 768 mph or 1,236 km/h).
Simplified: At a typical temperature like 70 degrees Fahrenheit (21.1 °C), the threshold value required for an object to be traveling at a supersonic speed is approximately 344 m/s, 1,129 ft/s, 770 mph or 1,238 km/h.