Speed in Air, Water & Solids at Any Temperature
Last reviewed: April 2026
A speed of sound calculator computes the velocity of sound waves in air at a given temperature, altitude, and humidity. The speed of sound increases with temperature — approximately 331.3 m/s at 0 degrees C and 343 m/s at 20 degrees C in dry air.
The speed of sound depends on the medium and its temperature. In air at 20°C, sound travels at 343 m/s (767 mph). The formula for air is: speed = 331.3 + 0.606 × temperature(°C). Sound travels faster in denser media — about 1,480 m/s in water and 5,960 m/s in steel. This is why you can hear a train through the rails long before the air-carried sound reaches you. For related physics calculations, see our Speed Distance Time Calculator and Wavelength Calculator.
Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 = speed of sound. Mach 2 = twice the speed of sound. Since the speed of sound varies with altitude and temperature, the same Mach number represents different absolute speeds at different conditions. At sea level (20°C), Mach 1 ≈ 767 mph; at 35,000 feet (−54°C), Mach 1 ≈ 660 mph. Fighter jets and supersonic aircraft use Mach numbers for airspeed.
Sound is a mechanical wave — it requires molecules to propagate. Higher temperatures mean molecules move faster and collide more energetically, transmitting the pressure wave more quickly. Each 1°C increase adds about 0.6 m/s to the speed of sound in air. This is why distant sounds can sometimes be heard better at night — temperature inversions create channels that bend sound waves back toward the ground.
| Medium | Speed (m/s) | Speed (mph) | Temperature |
|---|---|---|---|
| Air (20°C) | 343 | 767 | 20°C / 68°F |
| Air (0°C) | 331 | 741 | 0°C / 32°F |
| Water (25°C) | 1,497 | 3,349 | 25°C / 77°F |
| Steel | 5,960 | 13,332 | Room temp |
| Diamond | 12,000 | 26,843 | Room temp |
| Medium | Speed (m/s) | Speed (mph) | Temperature |
|---|---|---|---|
| Air (dry) | 343 | 767 | 20°C |
| Air (dry) | 331 | 740 | 0°C |
| Helium | 1,007 | 2,253 | 20°C |
| Water (fresh) | 1,480 | 3,312 | 20°C |
| Seawater | 1,533 | 3,430 | 25°C |
| Wood (oak) | 3,850 | 8,611 | — |
| Aluminum | 6,320 | 14,138 | — |
| Steel | 5,960 | 13,332 | — |
| Diamond | 12,000 | 26,843 | — |
In air, the speed of sound increases by approximately 0.6 m/s for each degree Celsius rise in temperature. The formula v = 331.3 + 0.606 × T (where T is in °C) provides accurate results for typical atmospheric temperatures. At 0°C, sound travels at 331.3 m/s. At 20°C, it reaches 343.2 m/s. At 40°C, it climbs to 355.5 m/s. This temperature dependence occurs because warmer air molecules move faster, transmitting the pressure wave more quickly. Humidity also affects sound speed slightly — moist air is less dense than dry air (water molecules are lighter than nitrogen and oxygen), so sound travels about 0.1–0.6% faster in humid conditions. Altitude affects sound speed only through its effect on temperature — at higher altitudes where air is cooler, sound travels more slowly.
Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 at sea level and 20°C is 343 m/s (767 mph), but at cruising altitude (35,000 feet, −55°C), Mach 1 is only about 295 m/s (660 mph) because the colder temperature reduces sound speed. Commercial airliners cruise at Mach 0.78–0.85, carefully staying below Mach 1 to avoid the dramatic increase in aerodynamic drag that occurs near the sound barrier. The Concorde cruised at Mach 2.04 (1,354 mph at altitude). Military fighters routinely exceed Mach 2, and the SR-71 Blackbird reached Mach 3.3 (2,193 mph). Hypersonic vehicles operate above Mach 5, where extreme heating from air compression becomes a dominant engineering challenge.
When an object exceeds Mach 1, it outruns the sound waves it produces, creating a cone-shaped shock wave called a Mach cone. Ground observers hear this as a sonic boom — a sharp double crack as the bow and tail shock waves pass over. The boom's intensity depends on the aircraft's size, speed, altitude, and atmospheric conditions. A fighter jet at 50,000 feet produces a boom of about 1–2 pounds per square foot (psf) of overpressure, enough to rattle windows but rarely cause damage. At lower altitudes, booms can exceed 5 psf and shatter glass. This is why supersonic flight over land is banned in the US and most countries. NASA's X-59 QueSST experimental aircraft aims to reduce sonic booms to quiet "thumps" of about 0.3 psf, potentially reopening commercial supersonic flight over populated areas.
Sound travels approximately 4.3 times faster in water than in air because water molecules are much closer together, transmitting pressure waves more efficiently despite being denser. In seawater, sound speed depends on temperature, salinity, and depth (pressure). The SOFAR channel — a layer at about 700–1,200 meters depth where sound speed reaches a minimum — acts as a natural waveguide that can transmit low-frequency sounds across entire ocean basins. Whales exploit this channel for long-range communication over thousands of kilometers. Sonar systems use sound speed in water to calculate distances: Time × Speed / 2 = Distance (dividing by 2 for the round trip). Navy sonar can detect submarines at ranges exceeding 100 miles under favorable conditions using this principle. For temperature-related calculations, see our Temperature Converter.
The most familiar application is estimating lightning distance: count seconds between lightning flash and thunder, divide by 5 for distance in miles (or by 3 for kilometers). At 343 m/s, sound takes approximately 2.94 seconds to travel 1 km or 4.73 seconds per mile. Sound speed matters for audio engineering — speaker placement in large venues must account for propagation delays, and digital audio processing adds latency measured in milliseconds that can cause noticeable echo if not compensated. In structural engineering, ultrasonic testing uses sound speed through materials to detect internal flaws in welds, castings, and concrete without destructive testing.
→ Remember: 5 seconds per mile for lightning. Count seconds from flash to boom, divide by 5 for miles. Each 5-second delay means the lightning is roughly 1 mile farther away.
→ Mach 1 changes with altitude. At cruising altitude (−55°C), Mach 1 is about 660 mph, not 767 mph. Always use local temperature for accurate Mach calculations.
→ Sound in solids is fastest. If you need to detect an approaching train, put your ear to the rail — sound travels through steel at 5,960 m/s versus 343 m/s through air.
See also: Speed Calculator · Wind Speed Converter · Temperature Converter · Wavelength Calculator
Musicians and audio engineers work with sound speed constantly, even when they do not realize it. The time delay between a stage monitor and the front-of-house speakers in a large venue must be compensated based on the speed of sound — a speaker 100 feet (30.5 m) from the stage introduces a 89-millisecond delay at 20°C. Digital delay processors add a corresponding 89 ms delay to the stage monitors so both sources arrive at the audience's ears simultaneously. Recording studios exploit sound speed for microphone placement: the "3:1 rule" ensures microphones are spaced at least 3 times the distance from the source to avoid phase cancellation. Room acoustics depend on reflections arriving at specific delays after the direct sound — early reflections (5–80 ms) contribute to perceived spaciousness, while later reflections become reverb. Concert halls are designed so that the first reflection arrives within 20–30 ms, and the reverberation time (RT60) falls between 1.5–2.5 seconds for orchestral music.
The Doppler effect causes the perceived frequency of sound to change when the source or observer is moving. An approaching ambulance siren sounds higher-pitched because sound waves are compressed, and a receding siren sounds lower-pitched because waves are stretched. The formula for perceived frequency is f' = f × (v + v_observer) / (v + v_source), where v is the speed of sound. At highway speeds (30 m/s), the frequency shift is approximately 9% — noticeable but not dramatic. Doppler radar used in weather forecasting applies the same principle with radio waves to measure the velocity of rain and wind within storm systems, enabling tornado detection and severe weather warnings.
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See also: Wavelength · Speed Distance Time · Noise Level · Dew Point · Density