At 20 °C sound travels at 343.3 m/s (1,236 km/h) in dry air; at 0 °C it slows to 331.4 m/s.
| Air temperature (°C) | °F | m/s | km/h | ft/s |
|---|---|---|---|---|
| -30 | -22 | 312.6 | 1,125.5 | 1,025.7 |
| -25 | -13 | 315.8 | 1,137.0 | 1,036.2 |
| -20 | -4 | 319.0 | 1,148.4 | 1,046.6 |
| -15 | 5 | 322.1 | 1,159.7 | 1,056.9 |
| -10 | 14 | 325.2 | 1,170.9 | 1,067.1 |
| -5 | 23 | 328.3 | 1,182.0 | 1,077.2 |
| 0 | 32 | 331.4 | 1,192.9 | 1,087.2 |
| 5 | 41 | 334.4 | 1,203.8 | 1,097.1 |
| 10 | 50 | 337.4 | 1,214.6 | 1,106.9 |
| 15 | 59 | 340.3 | 1,225.3 | 1,116.6 |
| 20 | 68 | 343.3 | 1,235.8 | 1,126.3 |
| 25 | 77 | 346.2 | 1,246.3 | 1,135.8 |
| 30 | 86 | 349.1 | 1,256.7 | 1,145.3 |
| 35 | 95 | 352.0 | 1,267.1 | 1,154.7 |
| 40 | 104 | 354.8 | 1,277.3 | 1,164.1 |
How it is computed
Speed of sound in dry air = 20.05 × √(T + 273.15) m/s, with T in °C, the same formula as the Mach number calculator. It depends on temperature only, not on air pressure; humidity adds a fraction of a percent.
FAQ
Does altitude change the speed of sound?+
Only through temperature. Pressure cancels out, so colder air at altitude is what makes sound slower up there.
How far away is lightning?+
Count the seconds between flash and thunder and multiply by about 343 m (at 20 °C): 3 seconds is roughly one kilometre.