Sound Travel Time Calculator
Example: 3 seconds = 1 km away
Why do you hear thunder after seeing lightning? Sound travels much slower than light, at about 343 metres per second in air at room temperature. This calculator shows how long sound takes to travel a given distance and how temperature affects its speed. It can be used to calculate thunder delays and echo times.
Elapsed time as sound travels
Travel Time
Speed of Sound
Echo Time (round trip)
How We Calculate This
Speed of sound in air: v = 331.3 + 0.606 × T (m/s), where T is temperature in Celsius. Travel time = distance / speed. Echo time = 2 × travel time. Other media use standard reference values.
Methodology last reviewed: April 2022. How SparkCalc works
Sources: NASA Glenn Research Center: Speed of Sound · NOAA National Weather Service: Understanding Lightning: Thunder · NOAA National Ocean Service: How Far Does Sound Travel in the Ocean?
Frequently Asked Questions
How do I calculate lightning distance?
Count the seconds between seeing lightning and hearing thunder. Each 3 seconds equals roughly 1 kilometre (or 5 seconds per mile). Light travels almost instantly, so the delay is entirely due to sound travel time.
Why does sound travel faster in water than air?
Sound travels by vibrating molecules. In denser materials like water and steel, molecules are closer together and transfer vibrations more efficiently, so sound travels faster despite the material being denser.
How does temperature affect sound speed?
Warmer air has faster-moving molecules that transfer sound vibrations more quickly. Sound speed in air increases by about 0.6 m/s for each 1°C rise in temperature.
Why do I see fireworks before hearing them?
Light travels at 300,000 km/s while sound travels at only 0.34 km/s in air. For fireworks 1 km away, you see them instantly but hear them about 3 seconds later.
Related Calculators
You might also find these calculators helpful: Speed Converter, and Length Converter.
Embed this calculator
Add this free calculator to your own website. Copy the code below and paste it into your page’s HTML. It is responsive and resizes to fit.