Speed of Sound Calculator

The Speed of Sound Calculator tells you how fast sound travels through air at any temperature — with an optional humidity correction — or through dozens of other media such as water, steel, helium and diamond. It reports the result in m/s, km/h, mph, ft/s and knots, shows the Mach 1 sound-barrier speed, how long sound takes to cover a distance, and how to use it to judge how far away a lightning strike is.

What Is the Speed of Sound?

The speed of sound is how fast a pressure wave — a vibration passed from molecule to molecule — travels through a material. In dry air at 20 °C (68 °F) it is about 343 m/s (1,235 km/h or 767 mph). Sound needs a medium to travel through, so unlike light it cannot move through a vacuum. It moves fastest in stiff, dense solids and slowest in gases.

Speed of Sound in Air Formula

In air the speed of sound depends almost entirely on temperature. The exact adiabatic relationship is:

where c is the speed of sound in metres per second and T is the air temperature in degrees Celsius. This comes from the physics relation \( c = \sqrt{\gamma R T / M} \), where \( \gamma \) is the adiabatic index of air (about 1.4), \( R \) is the gas constant, \( T \) is the absolute temperature in kelvin, and \( M \) is the molar mass of air. A handy linear approximation near room temperature is \( c \approx 331.3 + 0.606\,T \).

Moist air is slightly less dense than dry air, so sound travels marginally faster in it. The correction above (with RH the relative humidity in percent) adds at most about 1.2 m/s at 100% humidity — small, but included here for completeness.

Does Temperature Affect the Speed of Sound?

Yes — in air, temperature is by far the dominant factor. Warmer air molecules move faster and collide more often, passing the sound wave along more quickly. The speed rises by roughly 0.6 m/s for every 1 °C increase. This is why sound carries differently on a hot afternoon versus a cold night, and why Mach 1 is slower for a jet flying high in the cold upper atmosphere than near the warm ground. Air pressure and altitude on their own have almost no direct effect, because their influence on density and stiffness largely cancels out.

Speed of Sound in Different Media

Sound travels much faster in liquids and solids than in gases, because their molecules are packed closely and bound tightly, transmitting vibrations efficiently. The table below lists typical values at standard conditions.

Why Does Helium Make Your Voice Squeaky?

Sound travels almost three times faster in helium (about 1,007 m/s) than in air, because helium is far lighter than the nitrogen and oxygen in air. Your vocal tract resonates at higher frequencies when filled with this fast, light gas, shifting the timbre of your voice upward into the familiar "chipmunk" sound. (Inhaling helium is not safe — it displaces the oxygen you need to breathe.)

Using the Speed of Sound to Measure Distance

Because light reaches you almost instantly but sound lags behind, you can estimate how far away an event is by timing the delay:

• Lightning: Count the seconds between the flash and the thunder. Sound covers about 1 km every 3 seconds (1 mile every 5 seconds), so divide the delay by 3 for kilometres or by 5 for miles.
• Echoes & sonar: Send a pulse, time the round trip, and multiply by the speed of sound to find twice the distance to the reflecting surface.

What Affects the Speed of Sound?

How to Use This Calculator

1. Choose a mode: Select Air to calculate from temperature, or Other medium to look up a material.
2. Enter the conditions: For air, type the temperature and pick °C, °F or K, and optionally add a relative humidity. For a medium, choose it from the list.
3. Click Calculate: The tool computes the speed of sound instantly.
4. Review the results: See the speed in five units, the Mach 1 speed and a Mach table, sound travel times, the lightning rule, a comparison chart, a temperature-response curve, and a step-by-step breakdown.

Frequently Asked Questions

What is the speed of sound in air?

In dry air at 20 °C (68 °F) the speed of sound is about 343 m/s, which is 1,235 km/h or 767 mph. At 0 °C it is about 331 m/s. The speed rises by roughly 0.6 m/s for every degree Celsius increase in temperature.

How is the speed of sound in air calculated?

The speed of sound in dry air is c = 331.3 × √(1 + T / 273.15), where T is the air temperature in degrees Celsius. This is the exact adiabatic formula. Moist air is slightly faster, so an optional humidity correction of about 0.0124 m/s per percent of relative humidity can be added.

Does temperature affect the speed of sound?

Yes. In air the speed of sound depends almost entirely on temperature and rises as air gets warmer, because warmer molecules move faster and transmit the pressure wave more quickly. It increases by about 0.6 m/s for each degree Celsius. Air pressure and altitude on their own have almost no direct effect.

Why is the speed of sound faster in water and steel than in air?

Sound travels faster in stiffer, denser materials because their tightly bound molecules pass the vibration along more efficiently. It is about 1,481 m/s in water (over four times faster than air) and about 5,960 m/s in steel (roughly seventeen times faster than air).

How do I use the speed of sound to find how far away lightning is?

Count the seconds between seeing a lightning flash and hearing the thunder, then multiply by the speed of sound. As a rule of thumb sound travels about 1 km every 3 seconds, or 1 mile every 5 seconds, so dividing the delay in seconds by 3 gives the distance in kilometres and dividing by 5 gives it in miles.

What is Mach 1?

Mach 1 is the speed of sound in the surrounding medium. In air at 20 °C Mach 1 is about 343 m/s (1,235 km/h or 767 mph). Because the speed of sound changes with temperature, Mach 1 is slightly slower in cold air high in the atmosphere and faster in warm air near the ground.

Additional Resources

• Speed of Sound - Wikipedia
• Mach Number - Wikipedia