Speed of sound converter
Find how fast sound travels in air at a given temperature, or the temperature that gives a measured speed of sound.
Sound travels at 343.2 m/s: an echo returning after 1 second comes from 171.6 m away, and thunder takes 23.45 s to cross 5 miles.
What it means
How warm is that air?
Dry air, ideal gas: 331.3 √(1 + T/273.15) m/s. Humidity adds up to about 0.5 %; pressure has no effect.
Every unit
That air in every unit
Learn
Three things worth knowing
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331 + 0.6 T
Speed in m/s ≈ 331 + 0.6 × °C: 0 °C → 331, 30 °C → 349.
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Newton’s error
Newton calculated 298 m/s in 1687, too slow; Laplace fixed it in 1816 by noting the air heats as it is compressed.
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Thunder counting
Count 3 seconds per kilometer (5 per mile) between lightning and thunder: the light arrives instantly.
Shortcuts
Popular air temperature conversions
Background
About the speed of sound
Sound in air moves at about 343 m/s at 20 °C, but the speed depends on temperature, not pressure: about 0.6 m/s more for every degree. At the −56 °C of airliner cruise it is only 295 m/s, which is why Mach 1 is slower up there.