⚡ Lightning Distance Calculator
Count the seconds between seeing a lightning flash and hearing the thunder, then enter it here to estimate how far away the storm is.
The ‘flash to bang’ method
Because light travels essentially instantly while sound travels much slower, the delay between seeing a lightning flash and hearing its thunder tells you roughly how far away the strike occurred.
The formula
Distance = Speed of Sound × Time, using sound’s speed in air of approximately 343 m/s (at 20°C). This works out to roughly 1 mile for every 5 seconds of delay, or 1 kilometer for every 3 seconds, popular rules of thumb that follow directly from this formula.
The speed of sound varies slightly with air temperature and humidity, so this is an approximation, and lightning itself can strike many miles from where rain is falling. If thunder is heard at all, follow standard lightning safety guidance and seek shelter, since storms can be closer or moving faster than distance estimates suggest.