# Lightning Distance Calculator

Created by Hanna Pamuła, PhD
Reviewed by Bogna Szyk and Steven Wooding
Last updated: Jun 05, 2023

Imagine a cloudy, sultry summer afternoon. You see that the storm is approaching – suddenly, there's a dazzling lightning strike and, a few moments later, a deafening thunderclap. Are you in a safe place? How far away is the lightning? We may easily calculate the distance from the time difference between noticing the lightning flash and thunder.

If you are still unsure how to calculate lightning distance, keep reading and try the calculator!

## How to calculate the lightning distance?

Light travels at 186,291 miles per second (~300,000 km/s), and the speed of sound in dry air is equal to 0.21-0.22 miles per second (0.33-0.35 km/s), as it varies with the temperature.

We can notice the lightning almost immediately even though the storm is far from us, but the thunder needs around 5 seconds to travel one mile and approximately 3 seconds to travel one kilometer. Thanks to this seven orders of magnitude difference in sound and light propagation, we can easily estimate the storm distance:

Storm distance = Time × Speed of sound,

where Time is the number of seconds between noticing the flash and the thunder, and Speed of sound is the speed of sound in the air at a specific temperature. If you know how warm it was during that stormy day, you can check the speed value in our speed of sound calculator and use that exact number.

Did you notice that it's nothing else than a transformed simple formula for speed? For the more general formula for speed, view the speed calculator.

## Storm distance – how far away is lightning? ⛈️

The method of counting the seconds between lightning and thunder is sometimes called the flash-to-bang technique. So how far is the lightning?

1. Watch the stormy sky. Hopefully, you are at some distance from the thunderstorm, not in the middle!

2. As soon as you notice the lightning strike, count the number of seconds until you hear the thunder. Use your watch or phone, or try to count seconds as accurately as possible. Assume that, in our case, it's 15 seconds.

3. Calculate the storm distance. If you want to know approximately how far away the lightning is in miles, divide the number of seconds by 5; for kilometers, divide the seconds by 3. It will give us 3 miles or 5 kilometers.

4. Or simply use our lightning distance calculator, which can calculate it more accurately at the speed of light!

If you are keen on atmospheric studies, have a look at our dew point calculator.

## FAQ

### How do I calculate the distance of lightning in km?

To calculate the lightning distance in kilometers:

1. Note the time in seconds between the lightning flash and the thunderclap.
2. Divide the number of seconds by 3.
3. That's it! What you've found is the lightning distance in km.

### How do I calculate the distance of lightning in miles?

To calculate the lightning distance in miles:

1. Measure the time in seconds between the lightning flash and the thunderclap.
2. Divide the number of seconds by 5.
3. Well done. You've just measured the lightning distance in miles.

### What is the 30-30 rule for lightning?

When you see lightning, start counting to 30. If you hear the thunder before you finish counting, the thunderstorm is close enough to be dangerous, so seek shelter. Go outside only after 30 minutes from the last thunderclap.

### How long do I have to wait between thunder?

You must wait for at least 30 minutes after the last thunderclap as there may still be electric charges lingering in the clouds. This means there is still a chance of another lightning strike.

### How fast is a lightning bolt?

Lightning bolts travel at the speed of light, which is 186,291 miles per second (~300,000 km/s).

### Can lightning heat up the surrounding air?

Lightning can heat the air surrounding it to over five times the temperature of the sun's surface (around 30,000 °C).

Hanna Pamuła, PhD
Time between flash and thunder
sec
Storm distance
mi
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