By Becky Bolinger, Assistant State Climatologist and Research Scientist in Atmospheric Science, Colorado State University, and first published on

You probably do it. It might be ingrained from when you were a kid, and now it’s almost automatic. You see the flash of lightning – and you immediately start counting the seconds till it thunders.

But does counting really get you a good estimate for how far away the lightning is? Is this one of those old wives’ tales, or is it actually based on science? In this case, we have physics to thank for this quick and easy – and pretty accurate – calculation.

So what happens when a big storm rolls in?

The lightning you see is the discharge of electricity that travels between clouds or to the ground. The thunder you hear is the rapid expansion of the air in response to the lightning’s intense heat.

If you’re really close to the lightning, you will see it and hear the thunder simultaneously. But when it’s far away, you see and hear the event at different times. That’s because light travels much faster than sound. Think of sitting in the nosebleed seats at a baseball game. You see the batter hit the ball a second before you hear the crack of the bat.

The visual part is instantaneous. Pete Gregoire, CC BY

When observing an event on Earth, you see things almost the instant they happen – the speed of light is so fast you can’t even detect the travel time. The speed of sound is much slower, which gives us time to do our calculation.

Let’s simplify the speed equation: Sound travels a little over 700 miles per hour, or 700 miles in 3,600 seconds. That means 7 miles traveled every 36 seconds. Make this even easier and round down to 7 miles every 35 seconds… or 1 mile every 5 seconds! Count to 5: If you hear thunder, the lightning occurred within 1 mile.

Now that you know how far away that lightning strike was, is it far enough to be a safe distance from the storm? That’s actually a trick question. Thunder can be heard up to 25 miles away, and lightning strikes have been documented to occur as far as 25 miles from thunderstorms – known as a “bolt from the blue.” So if you can hear thunder, you’re close enough to be hit by lightning, and sheltering indoors or in an enclosed car is your safest bet.

And don’t count on the folk wisdom that lightning never strikes the same place twice to protect you. That one is just plain wrong. For example, lightning strikes the top of the Empire State Building an average of 23 times per year.


  1. I have seen ball lightening 3 different times in my life. Boy is it scary! Once at our open window on the end of our mobile home at the kitchen sink. My father had just walked over to the sink, got a glass of water, stood there drank it, and put the empty glass in the sink, he then turned to walk back toward our living room, and a ball of lightening rolled in the open window through the screen, and rolled around the sink then was gone. I yelled at my daddy to tell him what I had just witnessed. Two other times, I saw ball lightening rolling down power lines, once on 436 near where the power plant is near Arbys and the other time I witnessed it along Monroe St. rolling down the power lines then the ball of lightening jumped into a sable palm top setting it on fire! The ball lightening at 436 power lines looked bluish in color!

  2. We got caught in some very bad lightening one time while fishing at Lake Fairview on the back side, near where the old nightclub was, where the natural springs are, the south side. There was 3 of us in our small jon boat. We were away from the bigger boats and jet skis, out there fishing. One minute we were having so much fun, and all of a sudden, a storm moved in so fast, it wasn’t funny. Our trolling motor battery was getting low on charge, and we headed in, but the wind got up, and the white caps that had formed, were pushing us backwards. I was in the middle, my husband grabbed the paddle, and was in the front, and gave it all he had, to get us back in. Bigger motor boats were racing to get in, flying by us close, and about ran over us. The boy in the back of our boat, just kept the jon boat straight, for my husband to paddle. The worst was the cloud to ground lightening, and extremely loud thunder. I was down low with my head between my legs, and praying like I had never prayed before. Jet skis were coming toward us too, as it also started raining hard. It was a nightmare, and our jon boat was half full of water by the time we got back in. I truly thought we were goners. The weather can sure change things for you so fast!


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