Can you calculate how far away lightning struck by thunder?

It is possible to figure out how far away a lightning strike is with some simple math­.
It is possible to figure out how far away a lightning strike is with some simple math­.

Sound travels through air at "the speed of sound." Officially, the speed of sound is 331.3 meters per second (1,087 feet per second) in dry air at 0 degrees Celsius (32 degrees Fahrenheit). At a temperature like 28 degrees C (82 degrees F), the speed is 346 meters per second.

­As you can see, the speed of sound changes depending on the temperature and the humidity; but if you want a round number, then something like 350 meters per second and 1,200 feet per second are reasonable numbers to use. So sound travels 1 kilometer in roughly 3 seconds and 1 mile in roughly 5 seconds.


When you see the flash of a lightning bolt, you can start counting seconds and then divide to see how far away the lightning struck. If it takes 10 seconds for the thunder to roll in, the lightning struck about 2 miles or 3 kilometers away.

For more information on lightning and related topics, check out the links on the next page.


Originally Published: Apr 1, 2000

Lightning/Thunder FAQs

What causes thunder during lightning?
Thunder is basically the expansion of air that surrounds the lightning bolt’s path. As light travels very fast – around 186,282 miles per second – the heated air inside the clouds doesn’t get time to expand; thus, it gets compressed and raises the pressure and temperature. This creates rapid expansion, which produces sonic shock waves that result in thunder.
Can you calculate how far away lightning struck by thunder?
As you know the speed of sound is approximately 1,087 feet per second. When you see the thunder strike, count the time (in seconds) for which it lasts. For example, if the lightning struck for about 5 seconds, divide 1,087 by 5 to calculate the distance. Thus, you’ll get that the lightning struck around 217 feet away.
What should you not do during lightning?
To stay safe, avoid making unnecessary water contacts such as dishwashing, bathing, etc. That’s because lightning may get your plumbing. Moreover, avoid using electrical appliances and outlets like laptops, computers, stoves, dryers, etc. to make sure you stay safe.
Are you safe in a car during lightning storm?
Cars can be a safe place during a lightning thunderstorm due to their metal cage that surrounds people. However, you shouldn’t touch any metal parts of the car and pull over your vehicle near vulnerable areas. A general rule is to keep your hands restricted to your lap until the storm has passed.
Should I unplug everything during a thunderstorm?
The guidelines from the Department of Homeland Security say that it’s better to unplug everything during a thunderstorm because lightning strikes across electric poles might burst your home power lines.