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A thunderstorm is approaching, and suddenly you see lightning followed by a deafening clap of thunder. It sounded close  really close. Calculating the distance from lightning can just give you peace of mind if you're in a safe location, or it can help you know if you need to find a safe path as soon as possible. So how close were you to the lightning strike? Read on to find out.
Steps
Calculation Help
Method 1
Method 1 of 1:Calculating the Distance from Lightning

1Watch the sky for a flash of lightning.^{[1] X Research source }

2Count the number of seconds until you hear thunder. If you have a digital or analog watch, begin timing as soon as you see the lightning and stop as soon as you hear the thunder. If you don’t have a watch, do your best to count the seconds accurately. Say "One one thousand, two one thousand..." in your mind as you count.^{[2] X Research source }Advertisement

3Calculate the distance from lightning in miles or kilometers. Sound travels one mile every five seconds and one kilometer every three seconds. Therefore, if you want to find out how far you are from lightning, divide the number of seconds by 5 if you want the answer in miles and divide it by 3 if you want the answer in kilometers. The delay between when you see lightning and when you hear thunder occurs because sound travels much more slowly than light.^{[3] X Research source } Here's what you do:
 Let's say you counted 18 seconds. To find your distance from the lightning in miles, divide 18 by 5 to get 3.6 miles. To find your distance from the lightning in kilometers, divide 18 by 3 to get 6 kilometers.
 Though you won't be able to get a completely accurate result because the weather may vary in temperature and humidity, which will slightly affect the speed of sound, this is a good way to estimate how far you are from the lightning.

4Calculate the distance from lightning in feet or meters. Sound travels at a speed of about 344 meters, or 1,129 feet, per second. To calculate your distance from the lightning in meters, just round 344 down to 340 and multiply the number of seconds by 340. To calculate your distance from the lightning in feet, just round 1,129 up to 1130 and multiply the number of seconds by 1130. Here's how you do it:
 Let's say you counted 3 seconds. Multiply that number by 340 to get your distance in meters. 3 x 340 = 1020 meters. Multiply that number by 1130 to get your distance in feet. 3 x 1130 = 3,390 feet.
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Community Q&A

QuestionHow much power is in lightning?R2_d2000Top AnswererOne lightning strike is about a billion volts and can be between 10,000 to 200,000 amps.

QuestionHow is thunder caused?Community AnswerThunder is caused by the rapid expansion of air due to the extreme heat of lightning and thus creates a sonic boom (thunder) when it returns to its original state.

QuestionWhat is minimum distance that one cannot hear thunder after a lightning flash?Community AnswerThunder can be heard from a maximum distance of about 10 miles (16 km) under good atmospheric conditions.

QuestionIf lightning were to strike the water while I was swimming, at what depth would I be safe from being shocked?Community Answer273.54 ft. or 84.17 m in fresh water, approx. 18.74% shallower in salt water. Do not swim if there is lightning in the sky.

QuestionCan the equation predict where the lightning will strike?Community AnswerUnfortunately, you can never predict where the lightning will strike next. In fact, lightning doesn't always strike the area right beneath the thundercloud; it can strike as far as 10km away.

QuestionWhy does this rule work?Community AnswerWell, sound travels at a speed of about 344 meters, or 1,129 feet, per second. This means if we times a number of seconds between the flash and the sound and times it by 344 (or 340 to be rounded down) ,we can get a number of metres that lightning is!

QuestionIs it true that if I hear thunder, I could be struck by lightning?Community AnswerIf you hear thunder, it means there is a thunderstorm where you are or nearby, and yes, you could get struck by lightning. It is best to be inside when there is any sign of a thunderstorm.

QuestionHow do I calculate distance when it's just lightning?Community AnswerOther than a lightning detecting system, there is not a clear way of knowing how far away the lightning is.

QuestionDoes 5300 ft. in elevation change this?Community AnswerNot much. Light travels negligibly quicker at higher elevations due to there being fewer particles of air; in contrast, sound travels much more slowly due to less interaction between the particles of air that exist at high elevations.

QuestionIf a storm is 7.5 kilometers away, how much time is expected between observations of lightning and thunder?Community AnswerMultiply by 3 (since 1km/3 seconds) 7.5km*3 seconds = 22.5 seconds from lightning to thunder.
Tips
 If there are frightened children around, figure out how far away the strike is and tell them. This will help ease their fears and then they will most likely ask "How did you do that?"Thanks!
 Tell people about this method. Many people still believe the myth that the number of seconds you count is equal to the number of miles away the lightning is.Thanks!
 It can also be used to teach students how to calculate distance, speed and time.Thanks!
 Naturally, there is extensive room for error with this method. If possible, calculate the distance of several thunderclaps and average them for improved accuracy.Thanks!
 If you have a map and compass, try plotting the location of each lightning strike by drawing a line on the map in the direction of the lightning, and a cross at your calculated distance along this line.Thanks!
 If lightning strikes a point 1 mile away, you will see the strike approximately .00000536 seconds after the strike while you will hear it approximately 4.72 seconds after the actual strike. If you calculate the difference between these two experiences, a person will hear a strike approximately 4.71999 seconds after the strike actually occurred. Therefore, 5 seconds per mile is a fairly robust approximation.Thanks!
 Sound travels through air at slightly different speeds depending on air temperature and relative humidity. The difference is fairly small, however, and won’t substantially affect your calculations. For more information, see the sound speed calculators in the external links section below.Thanks!
Warnings
 If you find out that the lightning is less than a mile away, make sure you find/have shelter immediately. Lightning might strike you.Thanks!
 Due to the way sound travels and how various objects, such as mountains and buildings, interact with sound waves this is not the most reliable way to predict lightning distance. Don't let your life depend on it. Listen to local weather authorities.Thanks!
 If you do not see the lightning strike directly, the sound you hear may be a reflection off a building or a mountain, which adds time between the two events (the flash and the bang, thus making the lightning seem farther away than it really is. Consider the effect of nearby (especially large) objects/obstructions, as sound must "bend" around and bounce off of them. Any indirect path must be larger than the distance which you are trying to calculate.Thanks!
 Lightning can be deadly.^{[4] X Research source } See the related wikiHow article for more information on staying safe in a thunderstorm.Thanks!
 This is not an exercise to perform outside. If you are close enough to hear the thunder, you're close enough to be struck by lightning. Lightning can travel rapidly and has struck people over 10 miles away from the storm. If possible, find shelter immediately.^{[5] X Research source }Thanks!
References
 ↑ http://www.eo.ucar.edu/kids/dangerwx/tstorm6.htm
 ↑ http://www.eo.ucar.edu/kids/dangerwx/tstorm6.htm
 ↑ https://www.livescience.com/37734howfarawayislightningdistance.html
 ↑ https://www.weather.gov/media/safety/LightningBrochure18.pdf
 ↑ https://www.weather.gov/media/safety/LightningBrochure18.pdf
About This Article
To calculate the distance from lightning, watch the sky for lightning and then count the number of seconds after a lightning strike until you hear thunder. Take your response and divide it by 5 to determine the distance of the lightning strike in miles. For example, if you counted to 15 seconds before you heard thunder, divide 15 by 5 to get 3 miles. To calculate the distance in kilometers, divide the seconds by 3 instead. So, 15 divided by 3 would be 5 kilometers in distance. To learn how to calculate the distance in feet or meters, scroll down!
Reader Success Stories

"I had a lightning strike in my backyard. It hit a tree not far from the house, I immediately heard thunder and had a vague idea how to calculate miles but wanted to be sure. Especially in feet as I had a pretty good idea about miles. Your article helped!"..." more