What this calculator does
The speed of sound is not one fixed number the way the speed of light is; it depends on the medium it is travelling through and, for air, on temperature. Warmer air lets sound travel faster, because the air molecules are moving faster and pass the pressure wave along more quickly.
This calculator uses the standard approximation for dry air near sea level, v = 331.3 + 0.606 × T, where T is the temperature in degrees Celsius, to find the speed of sound at a given temperature, then uses that speed to work out either a travel time or a travel distance.
The formula
The formula 331.3 + 0.606T gives the speed of sound in air in metres per second, starting from 331.3 m/s at 0°C and rising by about 0.6 m/s per degree as the air warms. Once that speed is known, distance and time relate to it the same way they always do: distance equals speed times time, and time equals distance divided by speed.
| Term | Meaning |
|---|---|
| v | Speed of sound in air at the given temperature, in metres per second. |
| T | Air temperature in degrees Celsius. |
| 331.3 m/s | The speed of sound in dry air at 0°C, the constant this approximation is built from. |
The inputs explained
| Field | What to enter |
|---|---|
| Air temperature (°C) | The air temperature. Warmer air produces a higher speed of sound. |
| Also solve for | Choose whether to also work out a distance from a time, or a time from a distance. |
| Time (s) | The time taken, used when solving for distance. |
| Distance (m) | The distance covered, used when solving for time. |
When to use it
Estimating distance from a thunderclap
Counting the seconds between a lightning flash and the thunder, then multiplying by the speed of sound at the current temperature, gives a rough distance to the storm.
Working out a rifle or starting-gun delay
At a sporting event or shooting range, sound from a distant source reaches spectators noticeably later than the light or flash does; this calculator gives that delay for a known distance.
Checking a Mach number calculation
Mach number compares an object’s speed to the local speed of sound, so knowing the speed of sound at the relevant temperature is the starting point before working out how many Mach an aircraft or projectile is travelling at.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the speed of sound changes with air temperature
The speed of sound and the distance it covers in one second, across a range of temperatures.
| Air temperature | Speed of sound at this temperature | In km/h | Distance travelled in 1 s |
|---|---|---|---|
| -20°C | 319.18 m/s | 1,149.0 km/h | 319.18 m |
| -10°C | 325.24 m/s | 1,170.9 km/h | 325.24 m |
| 0°C | 331.30 m/s | 1,192.7 km/h | 331.30 m |
| 10°C | 337.36 m/s | 1,214.5 km/h | 337.36 m |
| 20°C | 343.42 m/s | 1,236.3 km/h | 343.42 m |
| 30°C | 349.48 m/s | 1,258.1 km/h | 349.48 m |
| 40°C | 355.54 m/s | 1,279.9 km/h | 355.54 m |
How long sound takes to cover different distances at 20°C
A range of distances at a fixed 20°C air temperature, solving for the time sound takes to cross each.
| Distance | Time to travel this distance |
|---|---|
| 100 m | 0.291 s |
| 343 m | 0.999 s |
| 500 m | 1.456 s |
| 1,000 m | 2.912 s |
| 3,430 m | 9.988 s |
| 5,000 m | 14.559 s |
Questions
What is the speed of sound?
In dry air at 20°C it is about 343 m/s, or roughly 1,235 km/h. It is not a single fixed constant like the speed of light; it changes with temperature, and it is different again in water or solid materials.
What is the speed of sound formula?
A common approximation for air near sea level is v = 331.3 + 0.606T, where T is the temperature in degrees Celsius and v comes out in metres per second. It is accurate enough for everyday estimates but does not account for humidity or altitude.
What is the speed of sound in km/h?
At 20°C, about 1,235 km/h. It rises with temperature: at 0°C it is around 1,193 km/h, and at 30°C it climbs to roughly 1,258 km/h.
Why does sound travel faster in warm air than cold air?
Sound moves through air as a pressure wave passed from molecule to molecule. Warmer air molecules move faster on average, so they transmit that pressure wave more quickly, which raises the speed of sound.
For the speed of light instead, and how far or long it takes to cross a distance, see the speed of light calculator. To compare an object’s speed against the local speed of sound, see the Mach number calculator.