Speed of Sound Calculator
Enter a temperature to see the speed of sound in dry air, fresh water, or seawater instantly. The calculator uses the standard acoustic formula for air and empirical equations for water, giving results in five common speed units. Switch to the reverse mode to find the air temperature that produces any target speed.
What is the speed of sound?
The speed of sound is the distance a sound wave travels through a medium per unit of time. It depends entirely on the mechanical properties of the medium, specifically its stiffness (or bulk modulus) and its density, and not on the loudness or frequency of the sound. In a more elastic, lower-density medium sound travels faster. This is why sound moves roughly four times faster through water than through air, and many times faster still through dense solids such as steel or aluminium.
How temperature affects speed in air
In dry air, temperature is the dominant variable. The standard formula is c = 331.3 x sqrt(1 + T / 273.15) m/s, where T is in degrees Celsius. At 0 °C the speed is 331.3 m/s; at 20 °C it rises to about 343 m/s. A useful linear approximation near room temperature is c = 331.32 + 0.606 x T, meaning every degree Celsius adds roughly 0.6 m/s. Pressure and humidity have small but measurable effects: a fully saturated air mass at 20 °C travels sound about 0.3-0.5% faster than dry air at the same temperature, because water vapour (lighter than nitrogen and oxygen) lowers the effective molecular mass.
Speed of sound in water and seawater
Fresh water at 20 °C carries sound at about 1481 m/s, roughly 4.3 times faster than air. Temperature still raises the speed, but the relationship is non-linear and peaks near 74 °C before declining. Salinity adds to the speed: every 1 psu increase raises it by about 1.3 m/s. Pressure (depth) also matters in the ocean: every 1000 m of depth adds roughly 17 m/s, creating a sound-speed profile that oceanographers use to track submarines and map seafloor features. The SOFAR channel (Sound Fixing and Ranging) is a depth layer where the combined effects of temperature and pressure create a speed minimum, trapping sound waves and allowing them to travel extraordinary distances.
Mach number and the sound barrier
Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 is exactly the speed of sound at the current conditions. Because the speed of sound changes with altitude and temperature, Mach 1 at sea level on a warm day (roughly 340 m/s) is faster in absolute terms than Mach 1 at 10,000 m altitude in the cold stratosphere (roughly 295 m/s). This matters for aircraft: an aircraft may be at Mach 0.85 at cruise altitude yet be moving slower in absolute terms than it would be at the same Mach number near the ground. The "sound barrier" refers to the drag and stability challenges that intensify as an aircraft approaches Mach 1, which were first broken by Chuck Yeager in October 1947.
Speed of sound in common materials (20 °C)
| Material | Speed (m/s) | Speed (ft/s) | Relative to air |
|---|---|---|---|
| Dry air (20 °C) | 343 | 1125 | 1x |
| Carbon dioxide | 267 | 876 | 0.78x |
| Helium (20 °C) | 1007 | 3304 | 2.9x |
| Fresh water (20 °C) | 1481 | 4859 | 4.3x |
| Seawater (20 °C) | 1521 | 4990 | 4.4x |
| Ice (0 °C) | 3838 | 12592 | 11.2x |
| Wood (oak) | 4000 | 13123 | 11.7x |
| Concrete | 4000 | 13123 | 11.7x |
| Brick | 3600 | 11811 | 10.5x |
| Aluminium | 6420 | 21062 | 18.7x |
| Iron | 5120 | 16798 | 14.9x |
| Steel | 5960 | 19554 | 17.4x |
| Glass (silica) | 5968 | 19580 | 17.4x |
| Diamond | 12000 | 39370 | 35x |
Approximate values at 20 °C (68 °F) and standard pressure. Solids can propagate both longitudinal and shear waves; values here are for longitudinal waves.
Frequently asked questions
Why does sound travel faster in warm air?
In warmer air, gas molecules move faster on average. Sound propagation depends on molecular collisions transferring energy, so faster-moving molecules pass the pressure wave along more quickly. Each degree Celsius of warming adds roughly 0.6 m/s to the speed of sound in dry air.
Does air pressure affect the speed of sound?
In an ideal gas, pressure and density change together in the same proportion, so their ratio (which determines sound speed) stays constant. In practice, moderate changes in atmospheric pressure have a negligible effect on the speed of sound in air. Temperature is the variable that matters.
Why does sound travel faster in water than in air?
Water is much less compressible (stiffer) than air, meaning pressure waves bounce back very quickly from displaced particles. Even though water is denser, the stiffness effect dominates, and the result is a speed of about 1481 m/s at 20 °C versus 343 m/s in air at the same temperature.
What is the speed of sound at standard conditions?
At 20 °C (68 °F) and standard sea-level pressure, the speed of sound in dry air is approximately 343.2 m/s (1235 km/h, 767 mph, 1125 ft/s, or 666 knots). The ISO standard reference often used in acoustics is 331.3 m/s at 0 °C (32 °F).
How can I use the speed of sound to measure distance?
Time how long it takes a sound (such as a thunderclap) to reach you after the event, then multiply by the speed of sound at the current temperature. For example, at 20 °C the speed is 343 m/s, so a 3-second delay means the source is about 1029 m away. This is the principle behind sonar, ultrasonic range finders, and the classic "count the seconds between lightning and thunder" technique.