Lightning Distance Calculator
Use thunder delay to estimate how far lightning struck
How to Use This Calculator
1
Watch for lightning
When you see a flash, start counting seconds.
2
Stop at thunder
Stop counting when you hear the thunder.
3
Press Calculate
Distance is shown in miles and kilometers.
Formula
Miles ≈ seconds / 5
Kilometers ≈ seconds / 3
Note: The speed of sound varies slightly with temperature and wind; these rules of thumb are close enough for safety awareness.
About Lightning Safety
If thunder roars, go indoors. Lightning can strike miles from a storm; seek shelter immediately if you can hear thunder.
- Avoid open fields and tall isolated objects
- Stay away from water and metal fences
- Wait 30 minutes after the last thunder before resuming activities
Frequently Asked Questions
Can lightning strike from clear skies?
Yes. "Bolt from the blue" strikes can occur several miles from a storm. Always take precautions.
Is counting seconds accurate?
It is an approximation for situational awareness, not a survey-grade measurement.