Speed of Sound Calculator
How fast does sound travel? It depends — mostly on temperature, but also on altitude, humidity, and the medium. This calculator goes beyond a static table: enter real conditions and get the speed of sound from physics, plus Mach number, echo ranging, and unit conversion.
Altitude uses the International Standard Atmosphere lapse rate (temperature falls 6.5 °C per 1,000 m up to 11,000 m). Humidity applies a small density correction — humid air carries sound slightly faster.
Regimes: subsonic below Mach 0.8 · transonic 0.8–1.2 · supersonic 1.2–5 · hypersonic above 5. For altitude effects, compute c in the Air tab first.
Helium is normalized to 965 m/s at 0 °C and hydrogen to 1,284 m/s at 0 °C, both scaled with √T like an ideal gas. Water and steel use standard reference values.
Sonar, bat echolocation, and ultrasonic rangefinders all use the same round-trip principle. Thunder distance works one-way: about 343 m per second of delay.
| Unit | Value |
|---|---|
| meters/second | – |
| kilometers/hour | – |
| miles/hour | – |
| feet/second | – |
| knots | – |
How it works
Speed of sound in common media
| Medium | Speed | vs air (20 °C) |
|---|---|---|
| Dry air, 0 °C | 331.4 m/s | 0.97× |
| Dry air, 20 °C | 343.3 m/s | 1.00× |
| Air at 10,000 m altitude | 299.5 m/s | 0.87× |
| Helium, 0 °C | 965 m/s | 2.81× |
| Hydrogen, 0 °C | 1,284 m/s | 3.74× |
| Fresh water | 1,480 m/s | 4.31× |
| Steel | 5,960 m/s | 17.36× |
Scope boundary
- This tool covers the speed of sound — mechanical waves that need a medium. It does not cover electromagnetic waves.
- A companion tool for the speed of light (#463) is planned as a separate tool and is intentionally out of scope here.
- Altitude uses the ISA standard profile, not live weather data; humidity uses a simplified ideal-gas mixture correction.
- Water and steel values are standard references at room conditions, not functions of temperature or pressure.
Frequently asked questions
What is the speed of sound in air?
At 20 °C (68 °F) and sea level, sound travels at about 343.3 m/s — roughly 1,236 km/h or 768 mph. At 0 °C it is slower, about 331.4 m/s. The exact value depends on air temperature: warmer air carries sound faster.
What is the formula for the speed of sound in air?
The standard formula is c = 20.05 × √T, where c is the speed in m/s and T is the absolute air temperature in kelvin (T = °C + 273.15). It comes from the physics relation c = √(γ·R·T/M): sound speed grows with the square root of absolute temperature.
Does temperature affect the speed of sound?
Yes. The speed of sound rises by roughly 0.6 m/s for every 1 °C increase in air temperature. That is why sound travels faster on a hot day (about 354.8 m/s at 40 °C) than on a freezing day (about 331.4 m/s at 0 °C).
How does altitude affect the speed of sound?
Because temperature falls with altitude, so does the speed of sound. Under the International Standard Atmosphere, T = 288.15 − 0.0065·h (for h below 11,000 m), giving about 320.6 m/s at 5,000 m and 299.5 m/s at 10,000 m — roughly 13% slower than at sea level.
Does humidity affect the speed of sound?
Slightly. Humid air is less dense than dry air, so sound travels a little faster — about 1.3 m/s faster at 20 °C and 100% relative humidity compared with perfectly dry air. The effect is small next to temperature.
What is the speed of sound in water?
About 1,480 m/s in fresh water — more than four times faster than in air. Sound travels faster in water because water is far less compressible than air, even though it is denser.
What is the speed of sound in steel?
About 5,960 m/s — roughly 17 times faster than in air. In general, sound travels fastest in solids, slower in liquids, and slowest in gases, because stiffer molecular bonds transmit vibrations more quickly.
What is the speed of sound in helium?
About 965 m/s at 0 °C (about 1,000 m/s at 20 °C) — nearly three times faster than in air. Lighter gas molecules move faster at the same temperature, which is also why your voice sounds squeaky after inhaling helium.
What is Mach number?
Mach number is the ratio of an object's speed to the local speed of sound: M = v/c. Mach 1 means exactly the speed of sound. Below Mach 0.8 is subsonic, Mach 0.8–1.2 is transonic, Mach 1.2–5 is supersonic, and above Mach 5 is hypersonic.
How do you calculate distance from an echo?
Use d = c × t / 2, where c is the speed of sound and t is the echo's round-trip time. You divide by two because the sound travels to the object and back. For example, a 0.5 s echo in 20 °C air means the object is about 85.8 m away.
How far away is lightning? What is the 3-second rule?
Count the seconds between the flash and the thunder, then divide by 3 to get the distance in kilometers (or multiply seconds by 343 for meters). This works because light arrives almost instantly while sound needs about 3 seconds to travel each kilometer.
Is there sound in a vacuum?
No. Sound is a vibration traveling through matter, so in a vacuum — with no air or other medium — there is nothing to carry it and the speed of sound is effectively zero.
What causes a sonic boom?
When an object moves faster than sound, the pressure waves it creates pile up into a cone-shaped shock wave. As that cone sweeps past you, you hear the sudden pressure jump as a sonic boom.
How fast is the speed of sound in km/h and mph?
At 20 °C, 343.3 m/s converts to about 1,235.8 km/h, 767.9 mph, 1,126.3 ft/s, or 667.3 knots. Use the unit converter tab above for any other temperature or unit.
Free tool by NRTechStudio