Speed of Sound Calculator
Find the speed of sound in air at any temperature, or in other gases, liquids and solids. Switch modes to work out how far away something is from an echo or from the delay between lightning and thunder, or how long sound takes to travel a distance.
How to use the Speed of Sound Calculator
- Choose a mode: speed of sound, distance from a delay, or travel time.
- Pick the medium. For air and other gases, enter the temperature.
- For a delay, enter the seconds and choose echo (there and back) or thunder (one way).
- Read the result in metric and imperial units with the working.
- Compare with the tables of speeds at other temperatures and in other materials.
Speed of sound formulas
- Dry air: v = 331.3 × √(1 + T ÷ 273.15) m/s, with T in °C. Close to room temperature, v ≈ 331.3 + 0.606 × T.
- Any ideal gas: v = √(γ R T ÷ M), where γ is the heat capacity ratio (1.40 for air, 5/3 for helium), R = 8.314 J/(mol·K), T is the absolute temperature in kelvin and M is the molar mass in kg/mol.
- Liquids and solids: v = √(K ÷ ρ) for liquids (bulk modulus over density); in solids, longitudinal waves depend on the elastic modulus and density.
- Distance from a delay: d = v × t one way (thunder), d = v × t ÷ 2 for an echo.
Speed of sound reference values
| Medium | Speed (m/s) | Speed (ft/s) |
|---|---|---|
| Air, −20 °C | 319 | 1,047 |
| Air, 0 °C | 331 | 1,087 |
| Air, 20 °C | 343 | 1,126 |
| Air, 40 °C | 355 | 1,164 |
| Helium, 20 °C | 1,007 | 3,304 |
| Carbon dioxide, 20 °C | ~267 | ~876 |
| Fresh water, 20 °C | 1,482 | 4,862 |
| Seawater, 20 °C | ~1,521 | ~4,990 |
| Lead | ~2,160 | ~7,090 |
| Copper | ~4,760 | ~15,600 |
| Steel | ~5,960 | ~19,550 |
| Aluminium | ~6,420 | ~21,060 |
Values for solids are longitudinal (compression) waves in bulk material and vary by alloy. Gas values in the calculator come from the ideal-gas formula and are within about 1% of measured values at ordinary temperatures.
Frequently asked questions
What is the speed of sound in air?
In dry air at 20 °C (68 °F) sound travels at about 343 m/s, which is 1,235 km/h, 767 mph or 1,125 ft/s. At 0 °C it is about 331 m/s. The speed depends mainly on temperature, not on air pressure.
How does temperature change the speed of sound?
In an ideal gas the speed is proportional to the square root of the absolute temperature: v = 331.3 × √(1 + T/273.15) m/s for air with T in °C. Near room temperature that is roughly 0.6 m/s faster for every 1 °C warmer.
How do I tell how far away lightning is?
Count the seconds between the flash and the thunder. Light arrives almost instantly, so the distance is the speed of sound times the delay: about 343 m per second, so roughly 3 seconds per kilometre or 5 seconds per mile.
How do I calculate distance from an echo?
An echo travels to the reflecting surface and back, so divide the round-trip distance by two: d = v × t ÷ 2. A 1-second echo at 20 °C means the wall or cliff is about 172 m away.
Why is sound faster in water and steel?
The speed of sound is √(stiffness ÷ density). Liquids and solids are far stiffer relative to their density than gases, so sound travels about 1,480 m/s in fresh water and about 5,960 m/s (longitudinal waves) in steel.
Does humidity affect the speed of sound?
Slightly. Humid air is a little less dense, so sound is faster by up to about 0.5% in very humid warm air. This calculator uses dry air, which is accurate enough for everyday use.
Is Mach 1 always the same speed?
No. Mach 1 is the local speed of sound, so it depends on the air temperature. At cruising altitude around −56 °C it is only about 295 m/s (1,062 km/h), compared with 340 m/s at sea level on a standard 15 °C day.