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Speed of Sound Calculator

Find the speed of sound in air.

Result

343.21 m/s

How it is calculated

Sound travels faster in warmer air. The tool uses v = 331.3 × √(1 + T / 273.15), with T the air temperature in °C and v in metres per second. 331.3 m/s is the speed at 0 °C and 273.15 is the offset from 0 °C to absolute zero. The square root comes from the fact that speed depends on the square root of absolute temperature. The formula is for dry air; humidity raises the speed slightly. Any temperature above −273.15 °C is accepted, though results far outside normal weather are only mathematical. Water, steel and other media are very different.

Worked example

The air temperature is 20 °C. First, T / 273.15 = 20 / 273.15 ≈ 0.0732, so 1 + 0.0732 = 1.0732. The square root is about 1.0360. Multiply by 331.3 and the speed of sound is 343.21 m/s, or about 1,235 km/h. At 0 °C it would be 331.3 m/s, so each extra degree adds roughly 0.6 m/s.

Try this example →

Common mistakes

  • Entering the temperature in °F or kelvin; the field uses °C only.
  • Applying the result to water or solids, where sound is several times faster.
  • Assuming the speed changes with air pressure; at a fixed temperature it does not (in ideal gas terms).
  • Forgetting that the value is in m/s, then comparing it to km/h speed limits.
  • Using the value to time lightning at a different temperature than the one entered.

About this calculator

This calculator uses v = 331.3 × √(1 + T/273.15) m/s, the standard approximation for how fast sound travels through dry air at temperature T (°C). It comes from the adiabatic relationship v = √(γRT/M), where γ is the ratio of specific heats for air and M its molar mass — since neither humidity nor pressure changes the result much at normal conditions, temperature alone is enough to get a good estimate.

Acousticians and audio engineers use it to time delay speakers and align microphone arrays, aviation and artillery calculations rely on it for sound-ranging (like the “flash-to-bang” thunder count), and physics students use it to check how pitch and echo timing shift between a cold morning and a hot afternoon.

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Comments (1)

  • Editorial team

    One everyday use is judging distance from a delay. At 20 degrees the speed is 343.21 m/s, so a three-second gap between a lightning flash and its thunder means roughly 1.03 km. For an echo, the sound travels there and back, so halve the distance. Light arrives effectively instantly, which is why the flash can start the clock. What are you timing, thunder, an echo or a sensor reading?

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