Lightning Distance Calculator
Calculate how far away lightning struck based on the seconds between the flash and thunder.
Lightning Distance
Lightning distance is calculated from the time delay between flash and thunder:
Distance = Time (seconds) × Speed of Sound
Speed of sound:
- 343 m/s (at 20°C / 68°F)
- 1,125 ft/s
- 767 mph
Unit conversions:
- 1 mile = 1,609 meters = 5,280 feet
- 1 kilometer = 1,000 meters = 0.621 miles
Quick rules of thumb:
- 5 seconds ≈ 1 mile (1.6 km)
- 3 seconds ≈ 1 kilometer
Safety: The “30-30 rule” — seek shelter if thunder follows lightning by less than 30 seconds (lightning is within 6 miles / 10 km). Stay sheltered for 30 minutes after the last thunder.
Why this works: Light travels at ~300,000 km/s (virtually instant), while sound travels at only ~343 m/s. The delay between seeing lightning and hearing thunder is caused entirely by the time it takes sound to reach you.