How to Tell How Far Away Lightning Is

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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.

Section 1 of 4:

Calculating the Distance from Lightning

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    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]
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    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]
    • 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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    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]
    • 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 2 of 4:

Why does thunder come after lightning?

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    When lightning strikes, it makes a noise! That noise is thunder. The noise actually happens at about the same time as the lightning, but you hear it several seconds after because sound moves slower than light. That means you see the lightning almost immediately because light moves super fast, but you hear the thunder later because sound moves more slowly, so it has to catch up. [4]
    • That’s why the longer you count between the lightning strike and the thunder, the farther away the lightning was—it took longer for the noise to reach you because it had to travel farther.
    • The speed of light is 299,792,458 meters per second, while the speed of sound is 343 meters per second.
Section 3 of 4:

What causes thunder and lightning?

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    Inside these clouds, droplets of water travel up, and ice crystals are pushed down. When they meet, tiny electrons (charged particles) are stripped away, separating the air into positively charged particles and negatively charged particles. When these areas of positive and negative get too strong, there’s a big discharge of electricity, causing lightning. [5]
    • Electricity wants to find the “path of least resistance” to get rid of its charge. That path often leads it down to the earth, though it often travels miles and miles through the air first.
    • Lightning itself travels at about 270,000 mph (430,000 km/h). [6]
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    The energy discharged by lightning is hot—about 50,000 °F (27,800 °C), which is 5 times hotter than the surface of the sun! This sudden heat makes the air burst out from the lightning, and then the air contracts super fast, making the “crack” noise we call thunder. [7]
    • When thunder makes a rumbling noise, that’s caused by the air continuing to vibrate after the first “crack.” If you only hear a rumble, the lightning is farther away.
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Section 4 of 4:

Staying Safe Around Lightning

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    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]
    • 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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    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]
    • 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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    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] While you’re out, pay attention for these signs of coming storms: [11]
    • 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

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  • Question
    How much power is in lightning?
    R2_d2000
    Top Answerer
    One lightning strike is about a billion volts and can be between 10,000 to 200,000 amps.
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  • Question
    How is thunder caused?
    Community Answer
    Thunder 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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  • Question
    What is minimum distance that one cannot hear thunder after a lightning flash?
    Community Answer
    Thunder 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]
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      • 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.
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      • Telling a frightened child how far away a lightning strike was can help ease their fears.
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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]
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      • 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]
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      References

      1. ↑ https://www.noaa.gov/jetstream/lightning/sound-of-thunder/learning-lesson-determining-distance-to-thunderstorm
      2. ↑ https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/thunder-and-lightning/thunder
      3. ↑ https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/thunder-and-lightning/thunder
      4. ↑ https://www.nssl.noaa.gov/education/svrwx101/lightning/
      5. ↑ https://scijinks.gov/lightning/
      6. ↑ https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/thunder-and-lightning/facts-about-lightning
      7. ↑ https://www.nssl.noaa.gov/education/svrwx101/lightning/
      8. ↑ https://scijinks.gov/lightning/
      9. ↑ https://www.cdc.gov/lightning/safety/index.html#cdc_preparedness_home_outside-outdoors
      1. ↑ https://www.noaa.gov/jetstream/lightning/lightning-safety
      2. ↑ https://www.brownsvilletx.gov/273/What-to-Do-Before-a-Thunderstorm
      3. ↑ https://wgntv.com/weather/weather-blog/ask-tom-why/whats-the-formula-to-calculate-the-distance-of-lightning/
      4. ↑ https://www.noaa.gov/jetstream/lightning/sound-of-thunder
      5. ↑ https://www.weather.gov/media/safety/Lightning-Brochure18.pdf

      About This Article

      Article Summary X

      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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