VERIFY | Yes, you can use time to measure how far away lightning is

WASHINGTON — The greater Washington D.C. area has seen its fair share of thunderstorms lately.

To decide if it is safe to remain outside, many people use the delay between the sight of lightning and the sound of thunder to determine how far away the lightning is.

THE QUESTION

Can you use the time between a lightning strike and the sound of thunder to determine the approximate distance of the lightning?

THE SOURCES

THE ANSWER

Yes, you can approximate the distance of lightning by counting the number of seconds until you hear thunder.

WHAT WE FOUND

Many children are taught that every second between the flash of lightning and the boom of thunder represents a mile of distance, but experts say that is not accurate.

According to the National Weather Service (NWS), it takes approximately five seconds for the sound of thunder to travel one mile. 

The National Aeronautics and Space Administration (NASA) says the speed of sound is 761 miles per hour at the standard temperature and pressure. That equates to 4.61 seconds per mile.

Since that is a nearly impossible amount of time for the human mind to estimate, rounding up to five seconds provides a close approximation.

But estimating the distance of lightning may not be the best way to protect yourself if you are determining when to move inside ahead of an approaching storm. The NWS says lightning can strike up to 25 miles away from the center of a storm. NWS recommends taking shelter at the first indication of a thunderstorm and remaining indoors until at least 30 minutes have passed since the last sound of thunder.

According to data from the National Oceanic and Atmospheric Administration's National Centers for Environmental Information, 33 people in Washington D.C., Maryland, or Virginia have been injured or killed by lightning in the last five years.