// by seankriegler.com
Lightning Distance Calculator
Calculate how far away lightning struck using the flash-to-thunder delay
See the flash → Start timer → Hear thunder → Stop timer
0.0 s
— or enter seconds manually —
⚠️ Loading...
-
Kilometres
-
Miles
-
Metres
-
Feet
// How It Works
Light travels at ~300,000 km/s (essentially instant). Sound travels at ~343 m/s at 20°C. The delay between flash and thunder tells you the distance.
// Temperature Effect
Sound speed = 331.3 + 0.606 × T(°C) m/s. At 0°C: ~331 m/s. At 30°C: ~349 m/s. Warmer air = faster sound = slightly shorter calculated distance.
// 30/30 Rule
If the flash-to-bang time is 30 seconds or less (~10 km), seek shelter immediately. Stay sheltered for 30 minutes after the last thunder.
// Safety Tips
Avoid open fields, tall trees, and water during storms. Get inside a building or hard-topped vehicle. Crouch low if caught outside — don't lie flat.