Speed of Sound & Light Calculator (Lightning Distance)
Calculate how far sound or light travels in a given time — including how far away lightning is from the delay before thunder — with sound speed adjusted for air temperature.
How to use
- 1Choose sound or light and enter the time.
- 2For sound, enter the air temperature for a more accurate speed.
How it's calculated
Speed of sound in dry air ≈ 331.3 + 0.606 × T(°C) m/s (343 m/s at 20 °C). Light: 299,792,458 m/s. Distance = speed × time.
Frequently asked questions
How do I estimate lightning distance?
Count the seconds between the flash and the thunder and divide by 3 for kilometres (or by 5 for miles).
When is lightning too close?
If thunder follows in under 30 seconds (about 10 km), go indoors — lightning can strike far from the storm.
Why does temperature change sound speed?
Warmer air molecules move faster and pass on vibrations more quickly.