Lightning Distance Calculator

About the Lightning Distance Calculator

Sound travels about 343 m/s, so counting the seconds between a lightning flash and the thunder gives the distance: roughly 3 seconds per kilometre (5 seconds per mile).

How to use

Enter the number of seconds between the flash and the thunder, then click Calculate.

Worked example

9 seconds → about 3 km (1.9 miles) away.

How to use this calculator

1. Measure the time between seeing the flash and hearing the thunder.
2. Divide that number of seconds by 5 to estimate the distance in miles.
3. Use the result as an estimate, since sound speed can vary with weather and terrain.

The formula explained

• \(\text{distance}\) = estimated distance to the lightning strike in miles
• \(\text{delay}\) = time between the flash and the thunder in seconds

Step by step method

1. Start timing when you see the lightning flash and stop when you hear the thunder.
2. Record the delay in seconds.
3. Divide the delay by 5 to estimate how many miles away the strike was.
4. Interpret the answer as an approximation, not an exact measurement.

Worked example

If you see lightning and hear thunder 15 seconds later, you can estimate how far away the strike was.

1. The delay is 15 seconds.
2. Use \(\text{distance} = 15 \div 5\).
3. That gives 3 miles.

Tips and common mistakes

• Count only the time between the flash and the thunder, not the time since you first noticed the storm.
• The result is an estimate in miles, so do not treat it as exact.
• If the storm is getting closer quickly, repeat the timing several times and watch whether the delay is shrinking.
• If you are outside and lightning is close, go indoors right away instead of continuing to measure.

Frequently asked questions