By Zencalcy Editorial TeamLast reviewed About us
The speed of sound is the rate at which a pressure disturbance travels through a medium. In air it depends mostly on temperature, rising by roughly 0.6 m/s for each degree Celsius. This page also handles the ideal-gas formula and the timing of an echo, where the pulse covers the distance to a reflector and back.
Sound speed in air, an ideal gas, or from an echo delay.
Air: a = 331.3 √(1 + T/273.15) Ideal gas: a = √(γ R T / M) Echo: a = 2 d / t
T is in kelvin for the gas formula (the air form takes Celsius), γ is the heat capacity ratio, R is 8.314 J/(mol·K), M is molar mass in kg/mol, d is one-way distance and t the total echo time.
| Symbol | Meaning |
|---|---|
| a | Speed of sound. |
| T | Temperature; Celsius in the air form, kelvin in the gas form. |
| γ | Ratio of specific heats, about 1.4 for air. |
| M | Molar mass of the gas. |
| d | Distance to the reflecting surface. |
| t | Round-trip echo time. |
a = 331.3 × √(1 + 20/273.15) = 343.2 m/s. An echo from a wall 100 m away returns after 2 × 100 / 343.2 = 0.583 s.
Continue with the String Harmonics Calculator, Sound Wavelength Calculator, or the Acoustic Impedance Calculator — or browse more acoustics and sound tools and all physics calculators.
Water vapour is lighter than dry air, so replacing some nitrogen and oxygen with H₂O lowers the average molar mass. The effect is small, a few tenths of a percent, but it matters for precise acoustic ranging.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026