# Thunder, lightning and distance. **URL:** \ **Category:** Factual Questions\ **Created:** [June 10, 2003, 3:25am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776 "2003-06-10T03:25:17Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![McDeath\_the\_Mad](https://avatars.discourse-cdn.com/v4/letter/m/a3d4f5/32.png) [@McDeath\_the\_Mad](https://boards.straightdope.com/u/McDeath_the_Mad)\ **Post date:** [June 10, 2003, 3:25am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/1 "2003-06-10T03:25:17Z")
Well I’m just witnessing one hell of a thunderstorm right now. It got me thinking, I was always told once you saw the sky “light-up” with lightning, you could count the seconds until the thunder sounded and you could tell how far away the lightning was. 1 second = 1 mile. Is there any truth to this? MtM ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 10, 2003, 3:29am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/2 "2003-06-10T03:29:46Z")
Actually, the rule-of-thumb is 5 seconds=1 mile. Which isn’t far off. Sound travels in air at STP at 1087 feet per second. There are 5280 feet in a mile, which works out to 4.86 seconds per mile. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [June 10, 2003, 3:32am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/3 "2003-06-10T03:32:29Z")
Not one second per mile but five seconds per mile. Sound travels at 331.29 meters per second (at a set temperature at a set air pressure at sea level yadda yadda), which is about 1,087 feet per second which is just over 1/5 of a mile. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [June 10, 2003, 3:35am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/4 "2003-06-10T03:35:22Z")
No, the speed of sound is about 776 mph (1,240 kph for non-Americans), or about 1,130 feet per second (340 meters per second), so it’s a little under five seconds per mile. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [June 10, 2003, 3:37am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/5 "2003-06-10T03:37:37Z")
Damn, you guys type fast. I just delayed a minute or two to check that I was right about 770mph. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [June 10, 2003, 3:40am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/6 "2003-06-10T03:40:11Z")
BTW: Here’s a cool calculator for the[Speed of Sound](http://www.measure.demon.co.uk/Acoustics_Software/speed.html) that let’s you correct for temp and humidity. (I used 21 C and 100% R.H. – because it was raining, according to the OP – to get my figures.) ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [June 10, 2003, 3:43am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/7 "2003-06-10T03:43:47Z")
Oh yeah, I wanted to add that the “No” in my first post was in response to the OP, not **tomndebb** or **Q.E.D.**. I may be a stickler for grammar, but what’s a few fps or mps among friends? ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [June 10, 2003, 3:45am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/8 "2003-06-10T03:45:11Z")
You should have taken the time to find a better source for your speed of sound. 😉 In 1986 it was recalibrated and found to be 331.29 meters per second (741.1 miles per hour) at 0° C at an air pressure of 1013.25 millibars (14.7 lb/sq ft) at sea level. (There was a lot of hoopla when an engineering or physics student rechecvked the numbers and discovered that the 1942 calculation had beenn in error.) ---
**Author:** ![Ficer67](https://avatars.discourse-cdn.com/v4/letter/f/c57346/32.png) [@Ficer67](https://boards.straightdope.com/u/Ficer67)\ **Post date:** [June 10, 2003, 3:49am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/9 "2003-06-10T03:49:31Z")
hard to believe that it took 44 years for someone to re-check that calculation. Ficer67 ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [June 10, 2003, 3:52am UTC](https://boards.straightdope.com/t/thunder-lightning-and-distance/180776/10 "2003-06-10T03:52:24Z")
Sorry. Cat on the keyboard is making me hit submit before he can change what I’ve typed and I’m missing some of the other posts. I suppose that if you want to be _realistic_ and consider real world temperatures and stuff, you can get different speeds. **Ficer67** : yeah, it was a really big surprise at the time.