Lightning Distance Calculator

Your details

Distance mode: enter seconds between flash and thunder to get storm distance. Time mode: enter a known distance to get the expected delay.
Start counting when you see the flash. Stop when you hear the thunderclap. Enter the elapsed seconds here.
s
Speed of sound rises about 0.6 m/s per degree Celsius. At 20°C it is 343 m/s; at 0°C it is 331 m/s. Leave at 20°C for the standard approximation.
°C
Storm distanceSeek Shelter
3.43km

Distance from your position to the lightning strike

Storm distance2.13mi
Speed of sound343.2m/s
Safety statusSeek shelter now - storm is within 10 km (6 mi)
3.43 km
Extreme danger<1.7Seek shelter1.7-5Shelter now (30-30 rule)5-10Monitor closely10-16Distant storm16+

The lightning struck about 3.43 km (2.13 mi) away.

  • Speed of sound at 20°C is 343.2 m/s - used to convert your 10s count.
  • The 30-30 rule: thunder within 30 seconds of a flash means the storm is close enough to be dangerous. Find shelter.
  • Wait at least 30 minutes after the last thunderclap before returning outdoors.

Next stepMove indoors or to a hard-topped metal vehicle now. Avoid tall objects, open fields, and water.

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