Speed of Sound Calculator
This speed of sound calculator works out the speed of sound in air from the temperature, in m/s and km/h, and turns a travel time into a distance, for example from lightning to thunder.
Example: Air temperature 20 °C · Travel time of the sound (optional) 3 s → Speed of sound: 343.2 m/s (1,236 km/h). Source: Wikipedia – Schallgeschwindigkeit (c = 331,3 m/s · √(1 + ϑ/273,15 °C), Luft). Updated: .
How it is calculated
At 20 °C the speed of sound in air is about 343 m/s, roughly 1,236 km/h (768 mph). In gases it depends on temperature, hardly on air pressure.
How it is calculated
For dry air c = 331.3 m/s · √(1 + ϑ / 273.15), where ϑ is the temperature in degrees Celsius. At 0 °C it is 331.3 m/s, and each extra degree adds about 0.6 m/s. A travel time t gives the distance s = c · t. For an echo the sound covers the path twice, so the obstacle is only half as far as the path travelled.
Uses
- Thunderstorms: count the seconds between lightning and thunder and find the distance.
- Echo and reverberation: estimate the distance to a wall from the delay.
- Physics lessons: check how temperature affects the speed of sound.
Frequently asked questions
How fast does sound travel in air?
About 343 m/s (1,236 km/h) at 20 °C and 331 m/s at 0 °C. The speed rises with temperature.
How do you work out how far away a storm is?
Seconds between lightning and thunder times the speed of sound. As a rule of thumb, three seconds is about one kilometre, five seconds about one mile.
Does the speed of sound depend on air pressure?
Almost not at all in air. Temperature and the gas composition matter.
How fast is sound in water?
About 1,480 m/s in fresh water at 20 °C, over four times as fast as in air. This calculator is for air only.
Sources and legal basis
- Wikipedia – Schallgeschwindigkeit (c = 331,3 m/s · √(1 + ϑ/273,15 °C), Luft)
- Wikipedia – Speed of sound (temperature dependence in air)
As of: · Editorial policy
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