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Figure out how close a lightning strike was
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You’ve probably been near a lightning strike that seemed close— really close. Calculating the distance from lightning can 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. We’ll show you how to calculate its distance from you, as well as answer your questions about thunder and lightning, and give you plenty of safety tips along the way.
Calculating Your Distance from a Lightning Strike
To tell how far away lighting is in miles, divide the number of seconds between the lightning flash and the thunder by 5 (or divide by 3 to find the distance in kilometers). If it takes 5 seconds to hear the thunder, the lightning is 1 mile away. If it takes 10 seconds, the lightning is 2 miles away.
Steps
Section 1 of 4:
Calculating the Distance from Lightning
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Count the seconds between the lightning and the sound of thunder. Once you see the flash, start counting. Start a timer on your phone, or count “One one thousand, two one thousand, three one thousand…” Stop counting the moment you hear the thunder, and remember how long it took. [1] X Research source -
Divide the time by 5 or 3 to find the distance in miles or kilometers. Sound travels 1 mile every 5 seconds, or 1 kilometer every 3 seconds. So, to find how far away the lightning struck, divide the time it took to hear thunder by 5 to find the distance in miles, or by 3 to find the distance in kilometers. [2] X Research source- Example: Say you counted 18 seconds. To find your distance from the lightning in miles, divide 18 by 5 to get 3.6 miles. For 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.
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Multiply the time by 1130 or 340 to find the distance in feet or meters. We can use the same idea to get a more precise estimate. Sound travels at a speed of about 344 meters, or 1,129 feet, per second. So we round 344 down to 340 and multiply the number of seconds by 340 to find distance in meters, or round 1,129 up to 1130 and multiply the number of seconds by 1130 to get distance in feet. [3] X Research source- Example: 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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Section 4 of 4:
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Stay inside during thunderstorms, if possible. If you can hear thunder, it’s dangerous to be outside. Head indoors for protection , and stay there until the storm has passed. You might also shelter in a vehicle or under a pavilion, if you can’t get inside. [8] X Research source- Remember the 30-30 rule: Count the time between the lightning and thunder. If it’s less than 30 seconds, go inside immediately, and only come out 30 minutes after the last sound of thunder.
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Stay away from tall objects when outside. If you can’t get inside, head downhill to get off of any hills or mountains to avoid getting struck . Stay away from tall or metal objects like trees or telephone poles. Sit on the ground with your knees tucked and your head down, with your hands over your ears, but never lie flat on the ground—this may attract electric shock through ground currents. [9] X Trustworthy Source Centers for Disease Control and Prevention Main public health institute for the US, run by the Dept. of Health and Human Services Go to source- If you’re in a forest, take shelter under lower trees.
- Tell your group to spread out. Lightning is more attracted to large groups.
- Stay away from bodies of water like lakes or rivers.
- If you’re in or on the water, get out immediately. If you're in a boat, take shelter under a roof, and stay away from the sides of the boat.
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Plan your outside time around the weather. The best way to stay safe from thunderstorms is to plan accordingly. Check the forecast for your activity or trip, and avoid spending time outside during stormy days. [10] X Research source While you’re out, pay attention for these signs of coming storms: [11] X Research source- Large, dark clouds on warm days, particularly in the afternoon.
- Sudden drops in temperature, especially in the mountains
- Sudden gusts, or related weather like rain or even snow.
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Calculation Help
Community Q&A
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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.
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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.
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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.
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Tips
- Many people still believe the myth that the number of seconds you count is equal to the number of miles away the lightning is. Let them know the real way! [12] X Research sourceThanks
- Using this math, if it takes 5 seconds to hear thunder, lightning is about 1 mile away. 15 seconds equates to 3 miles, and 0 seconds means the lightning is very close to you.Thanks
- Telling a frightened child how far away a lightning strike was can help ease their fears.Thanks
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Warnings
- Due to the way sound travels and how various objects, such as mountains and buildings or even air density, interact with sound waves, this is not the most reliable way to predict lightning distance. Listen to local weather authorities, instead. [13] X Research sourceThanks
- 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. [14] X Research sourceThanks
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References
- ↑ https://www.noaa.gov/jetstream/lightning/sound-of-thunder/learning-lesson-determining-distance-to-thunderstorm
- ↑ https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/thunder-and-lightning/thunder
- ↑ https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/thunder-and-lightning/thunder
- ↑ https://www.nssl.noaa.gov/education/svrwx101/lightning/
- ↑ https://scijinks.gov/lightning/
- ↑ https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/thunder-and-lightning/facts-about-lightning
- ↑ https://www.nssl.noaa.gov/education/svrwx101/lightning/
- ↑ https://scijinks.gov/lightning/
- ↑ https://www.cdc.gov/lightning/safety/index.html#cdc_preparedness_home_outside-outdoors
- ↑ https://www.noaa.gov/jetstream/lightning/lightning-safety
- ↑ https://www.brownsvilletx.gov/273/What-to-Do-Before-a-Thunderstorm
- ↑ https://wgntv.com/weather/weather-blog/ask-tom-why/whats-the-formula-to-calculate-the-distance-of-lightning/
- ↑ https://www.noaa.gov/jetstream/lightning/sound-of-thunder
- ↑ https://www.weather.gov/media/safety/Lightning-Brochure18.pdf
About This Article
Article Summary
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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!
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- "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
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"Calculating the distance of how far away a thunderstorm is. I always thought it was divide by 2, but now I know it is divide by 5. I'm passing this onto my grandkids. Thank you so much."
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