Calculating the Distance to Lightning Strikes
June 21, 2011 at 2:00 am Chad Upton 8 comments
By Chad Upton | Editor
I love watching electrical storms. The time between strikes builds anticipation; the light show is epic and the sound is awe inspiring.
As a kid, I heard that if you count the seconds between the sight of the lightning and the sound of the thunder, the distance to the strike is one mile for every second you count. It’s a simple model, but it’s far from accurate.
It’s actually closer to 5 seconds for every mile.
For those who don’t know, you see the lightning before you hear the thunder because light travels much faster than sound, about 200,000 km per second faster (186,282 miles per second).
Depending on the environment, sound travels at about 350 meters per second (1150 feet per second). To calculate the distance, you can multiply the number of seconds by the speed of sound in your preferred units above.
If you count 10 seconds between the lightning and the thunder, the strike was about 3.5 km (2.17 miles away). To make it easier, use this lightning distance calculator.
Thanks to Kristen for this suggestion.
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Image: John Fowler (cc)
Sources: Lightning Strike Distance Calculator, Wikipedia (Speed of Light, Speed of Sound)
Entry filed under: Despite Popular Belief. Tags: calculate, distance, lightning, storm, strike, thunder.
Broken Secrets 
1.
Niina | June 21, 2011 at 9:31 am
I always count the seconds and then share them in three which then gives me the distance in kilometers. I think it’s easier than multiplying (I suck at math) and the result is close enough. :)
2.
Elbyron | June 22, 2011 at 11:08 am
The problem with dividing by 3 is that the number of seconds you counted isn’t always evenly divisible by 3. If you counted 5 seconds, and you suck at math, how are you going to know that the answer is 1.67km? Sure you can always estimate and say “it’s one to two kilometers away”, but that doesn’t sound as smart as knowing the right answer. So here’s an easy way to multiply by 0.35 and get a fairly accurate distance:
a) Multiply the number of seconds by 3, this should be easy since it’s usually less than 10 seconds. If you have trouble with your three-times-tables, just add the number to itself twice, i.e. 8 + 8 =16, + 8 = 24
b) Now halve the number of seconds and add it to the total from step a. If it doesn’t divide evenly in two, just round it up (9 / 2 = 5).
c) Now just divide the total by 10, by simply moving the decimal place once to the left.
So if you counted 7 seconds, you would get 21 from step a, plus 4 from step b, which equals 25, and with step c your final answer becomes 2.5km.
Of course, if you have a calculator and stopwatch on your cell phone, you can get a much more accurate answer.
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4.
Elbyron | June 22, 2011 at 11:31 am
I’d also like to point out that the estimated speed of sound shown here as 350m/s, is only applicable to sound at air temperatures of about 32°C (90°F). Though the ground temperature could be this high during a thunderstorm, the source of the thunder is many kilometres high, where temperatures are considerably cooler. At 2°C, the speed of sound is 332.66m/s in dry air. Having humidity of 90% will increase that slightly, making it exactly 333m/s and thus exactly 3 seconds per kilometer. So Niina, though your method of dividing by 3 may be difficult for some values, it is actually quite accurate!
5.
gwendolynbrianna | July 31, 2011 at 1:48 pm
i once had a lighting strike in which the count between light and sound was zero…. you guessed it it struck our house
from then on i don’t count anymore….we”ll see what happens
6.
nameless | August 2, 2011 at 6:17 am
My neighbors lost 2 trees to lightning last week. I didn’t get a chance to start counting.
7.
khayombe | December 5, 2012 at 7:33 am
get serious with life.
8.
Yeesha | September 4, 2013 at 11:03 pm
Thanks so much! This helped me with my homework! Really helpful info. :)