# Re: Why manhole covers are round **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [December 10, 2003, 12:22am UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043 "2003-12-10T00:22:46Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![beta522](https://avatars.discourse-cdn.com/v4/letter/b/b77776/32.png) [@beta522](https://boards.straightdope.com/u/beta522)\ **Post date:** [December 10, 2003, 12:22am UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/1 "2003-12-10T00:22:46Z")
Maybe I’m missing something here, but I’d like to comment on the reason that Cecil says manhole covers are round. Simply put: to keep them from falling in. I bring this up again because the question was listed in the MENSA quiz section of American Way Magazine. Mentioned in the vein that “if you can answer this, you’re the smartest person in the world and you belong in MENSA.” Having read the post, I thought to myself “they’re round so they won’t fall in stupid!” But I got to thinking and went back and reread the column. It seems to me that what keeps the cover from falling in isn’t it’s “roundness,” but rather the inch or so wide lip below the hole that hold the cover. I submit that if the hole were 18" or so around and didn’t have a lip, the cover would fall straight through. Right? What else would possibly keep it in place? For that matter, it wouldn’t make any difference what shape the cover or the hole was, so long as there was a lip for it to sit on. If it were square and had a lip, and you turned the cover on end diagonally, wouldn’t it just wedge in the hole? Inconvenient, no doubt, but it wouldn’t fall in. Would it? I plan to make a mock-up at work tomorrow! ---
**Author:** ![yguy](https://avatars.discourse-cdn.com/v4/letter/y/eb9ed0/32.png) [@yguy](https://boards.straightdope.com/u/yguy)\ **Post date:** [December 10, 2003, 3:34am UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/2 "2003-12-10T03:34:29Z")
If the cover and hole were square with a lip, one can see that the cover could drop through easily if it were held centered avove the hole, and at a 45 degree angle to the sides of the hole with one edge plumb. With a round hole that’s impossible, no matter how the cover is oriented with respect to the hole. ---
**Author:** ![AmbushBug](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ambushbug/32/4600_2.png) [@AmbushBug](https://boards.straightdope.com/u/AmbushBug)\ **Post date:** [December 10, 2003, 8:38am UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/3 "2003-12-10T08:38:56Z")
You forgot the obligatory [link](http://www.straightdope.com/classics/a1_247a.html) to the column. Besides, you’re all wrong. Manhole **covers** are round because **manholes** are round. Duh. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [December 11, 2003, 2:43pm UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/4 "2003-12-11T14:43:14Z")
[A previous thread](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=203759&highlight=manhole) where some discussion on why _manholes_ might be round. ---
**Author:** ![5cents](https://avatars.discourse-cdn.com/v4/letter/5/46a35a/32.png) [@5cents](https://boards.straightdope.com/u/5cents)\ **Post date:** [December 11, 2003, 4:36pm UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/5 "2003-12-11T16:36:10Z")
> [@](#): > > \*Originally posted by beta522 \* > **But I got to thinking and went back and reread the column. It seems to me that what keeps the cover from falling in isn’t it’s “roundness,” but rather the inch or so wide lip below the hole that hold the cover. I submit that if the hole were 18" or so around and didn’t have a lip, the cover would fall straight through. Right? What else would possibly keep it in place? For that matter, it wouldn’t make any difference what shape the cover or the hole was, so long as there was a lip for it to sit on. If it were square and had a lip, and you turned the cover on end diagonally, wouldn’t it just wedge in the hole? Inconvenient, no doubt, but it wouldn’t fall in. Would it? I plan to make a mock-up at work tomorrow!** You are right, the lip does hold the cover up. However… Lets say you have a 24" round cover. If the hole is 22" diameter (i.e. 1" lip), the cover will never fall in. Now lots say you have a 24" square cover and a hole that is 22" square. The diagonal is about 31". Last time I checked, you can toss something that is 24 inches wide down a hole that is 31 inches wide. So the real answer is that the lip holds the cover up, but that with a circle you can use a minimal lip, and the cover will never fall through. You can design a square cover so that it will never fall through, but you’ll need a bigger lip. Given a 24" square cover, a 4" lip (16" hole) would do the trick. Am I a genious or what? ---
**Author:** ![cdhostage](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@cdhostage](https://boards.straightdope.com/u/cdhostage)\ **Post date:** [December 13, 2003, 9:28am UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/6 "2003-12-13T09:28:11Z")
It’s impossible to drop a manhole cover through a manhole, through excessive stupidity or through maliciousness. That’s it - covers are made very heavy (auto traffic has to pass over them safely), so no one’s going to do something on the spur of the moment with a manhole cover. ---
**Author:** ![I\_Love\_Me\_Vol.I](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/i_love_me_vol.i/32/521_2.png) [@I\_Love\_Me\_Vol.I](https://boards.straightdope.com/u/I_Love_Me_Vol.I)\ **Post date:** [December 13, 2003, 10:31am UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/7 "2003-12-13T10:31:57Z")
cdhostage— perfect. that’s all there is to it. Ergo the shape. bye, thanks, ---
**Author:** ![Mhernan](https://avatars.discourse-cdn.com/v4/letter/m/d2c977/32.png) [@Mhernan](https://boards.straightdope.com/u/Mhernan)\ **Post date:** [December 13, 2003, 1:52pm UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/8 "2003-12-13T13:52:11Z")
:wally You should have stuck wi th the round and left it there, or you could have said that if the manhole cover were rectangular, or oval it could fall in the hole and you would prbably lose your job. Yeah, that the answer, manhole covers are round, otherwise you would lose your job. ---
**Author:** ![Raxel](https://avatars.discourse-cdn.com/v4/letter/r/9de053/32.png) [@Raxel](https://boards.straightdope.com/u/Raxel)\ **Post date:** [December 13, 2003, 10:18pm UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/9 "2003-12-13T22:18:47Z")
They’re round because circles have no edges…if u cant figure it out frum that ---
**Author:** ![Mhernan](https://avatars.discourse-cdn.com/v4/letter/m/d2c977/32.png) [@Mhernan](https://boards.straightdope.com/u/Mhernan)\ **Post date:** [December 13, 2003, 10:24pm UTC](https://boards.straightdope.com/t/re-why-manhole-covers-are-round/218043/10 "2003-12-13T22:24:43Z")
Let me tell you something Raxel. I don’yuse manhole coverss I have Womenhole coversand just incase you can’t flegur thet wun out, they’re rectangular, and, check this out, they have lips on the edges too.