Lightning Distance Calculator
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.
How to use Lightning Distance Calculator
- Count the seconds between the flash and the thunder.
- Enter that number of seconds.
- Read how far away the lightning struck.
- Check the warning on whether the storm is a threat.
Frequently asked questions
How does it turn seconds into distance?
It multiplies the seconds between flash and thunder by the speed of sound, about 343 meters per second, so every 3 seconds is roughly 1 kilometer or every 5 seconds about 1 mile.
Why count the delay between flash and thunder?
Light reaches you almost instantly while sound travels much slower, so the gap between seeing the flash and hearing thunder scales with distance to the strike.
When is a storm close enough to be dangerous?
By the 30 30 rule, if thunder follows the flash within 30 seconds, roughly 10 kilometers, the storm is close enough that you should seek shelter.
What is Lightning Distance Calculator?
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.
Is Lightning Distance Calculator free to use?
Yes. Lightning Distance Calculator is completely free, with no sign-up and no usage limits.
Does Lightning Distance Calculator work in a web browser?
Yes. Lightning Distance Calculator runs in any modern web browser. There is nothing to download or install.
Is my data private with Lightning Distance Calculator?
Yes. Lightning Distance Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.
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Link this tool from a README, doc or site. The badge links back to this page.
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