Lightning Distance Calculator

Estimate how far away lightning struck from the thunder delay.

Flash-to-thunder time

Speed of sound

Distance 0.0021

Distance 0.0008

Formula: distance = time × speed of sound

Step-by-step with your numbers:

1. Values used:

2. Flash-to-thunder time = 6

3. Speed of sound = 343

5. Distance = 0.0021

6. Distance = 0.0008

Did we solve your problem today?

Light arrives instantly but thunder lags, so the delay reveals the distance.

The math behind it

distance = delay × speed of sound. A rough rule: every 3 seconds ≈ 1 km (5 seconds ≈ 1 mile).

6 s delay → about 2.06 km away.

When is it dangerous?

If thunder follows within 30 seconds (~10 km), seek shelter immediately.