Question 1

How do you calculate lightning distance?

Accepted Answer

Count the seconds between seeing the lightning flash and hearing the thunder. Divide by 5 to get the distance in miles, or divide by 3 to get the distance in kilometers. This works because light travels almost instantly while sound takes about 3 seconds per kilometer.

Question 2

What is the 30/30 rule for lightning safety?

Accepted Answer

If the time between lightning and thunder is 30 seconds or less, the storm is close enough to be dangerous — seek shelter immediately. Wait at least 30 minutes after the last thunder before resuming outdoor activities.

Question 3

Why does temperature affect the calculation?

Accepted Answer

The speed of sound in air varies with temperature — approximately 331 m/s at 0°C increasing by about 0.6 m/s per degree. This calculator adjusts the speed of sound based on the air temperature you enter for greater accuracy.

Question 4

Is it safe to be outside during a lightning storm?

Accepted Answer

No. If you can hear thunder, you are within striking distance of lightning. Move indoors or into a hard-topped vehicle immediately and avoid open areas, tall objects, and water.