When you see a lightning flash and then hear thunder, the delay tells you how far away the strike was, because light reaches you almost instantly while sound travels at roughly 343 meters per second. This is the classic flash to bang method, and it is a genuinely useful safety tool: if the gap is thirty seconds or less the storm is within about ten kilometers and close enough to strike you, the widely taught threshold for seeking shelter. This calculator turns the number of seconds you counted into a distance in kilometers and miles, using the speed of sound at typical air temperature. Enter the seconds between the flash and the thunder and read the distance along with a plain safety note. Remember the thirty thirty rule: shelter when the delay drops to thirty seconds, and wait thirty minutes after the last thunder before heading back out. Everything runs locally in your browser for instant, private results.
When you see a lightning flash and then hear thunder, the delay tells you how far away the strike was, because light reaches you almost instantly while sound travels at roughly 343 meters per second. This is the classic flash to bang method, and it is a genuinely useful safety tool: if the gap is thirty seconds or less the storm is within about ten kilometers and close enough to strike you, the widely taught threshold for seeking shelter.
Yes. Lightning Distance Calculator is completely free, with no sign-up and no usage limits.
Yes. Lightning Distance Calculator runs in any modern web browser. There is nothing to download or install.
Yes. Lightning Distance Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.